- "They say Nero sang as he watched Rome burn. Now I understand why. If only Shado were here to witness this."
- —Slade Wilson[src]
The Siege was a terrorist attack that took place in Starling City led by Slade Wilson to take away everything Oliver Queen loved. The plan was executed using an army of Mirakuru-enhanced soldiers to lay waste to the city and destroy it. The plan was opposed by Team Arrow with aid from the League of Assassins and the SCPD. The plan was partially successful, but led to Slade's incarceration on Lian Yu.
During Oliver Queen's exile on Lian Yu, he, Slade Wilson, Sara Lance, and Shado came into conflict with the mad scientist Dr. Anthony Ivo, a man who was determined to locate the famed Mirakuru serum to heal his ailing wife. During this conflict, Slade was almost killed and the group was forced to use the serum on him to save his life.
The other three were captured by Ivo not long after, with Ivo forcing Oliver to choose which of the other two to spare and which to have him kill. When Oliver couldn't make a decision, Ivo pointed the gun at Sara, forcing Oliver to jump in front of it. Ivo took that as a decision and murdered Shado in front of them.
Slade, who barely survived the Mirakuru injection and who loved Shado despite her affections for Oliver, came to blame Oliver for Shado's death due to Ivo's manipulation and the rage side effect of the Mirakuru. Vowing to destroy everything Oliver loved, the two came to blows after Slade appeared to have killed Sara and destroyed the Mirakuru cure Ivo created.
Oliver barely came out on top due to Slade's superhuman strength and pain resistance. However, when Slade taunted him by saying that he would pay his sister a visit, Oliver chose to kill Slade instead of curing him, stabbing him in the eye with an arrow.
Slade managed to survive and swam as far as he could while the Mirakuru kept healing all of his injuries (except for his missing eye), eventually being rescued. For a while, he rejoined ASIS and spent time with his son while training new recruits.
Learning of Oliver's survival triggered the Mirakuru's rage once more, however, and he stole a set of armor (which later became his Deathstroke suit), sparing only his son in his rampage. After escaping, he quickly used his skills and superhuman abilities to become a well known mercenary, codename Deathstroke, all while planning his revenge against Oliver.
Rise of Brother Blood
Shortly after The Undertaking, an Alderman named Sebastian Blood quickly rose in popularity in the Glades due to his passion and charisma, particularly regarding the attitudes of the rich towards the poor. These positive attributes were used to mask his double life as Brother Blood, leader of the Church of Blood and ally to Slade Wilson.
Slade offered Sebastion the role of Mayor of Starling City in return for his help, to which Sebastian agreed. To that end, Slade had the Hoods assassinate the Mayor, not only creating the need for an election but also catching the attention of the recently returned Oliver Queen.
Taking down the Hoods, as well as the Bronze Tiger, gave Oliver's alter ego “The Arrow” a more positive viewing in the public eye than he previously had. However, he failed to show up to a benefit event as a result of his vigilante activities, resulting in Sebastian publicly criticizing him and saying that he was not a friend to the people of his city.
Oliver and Sebastian later made amends due to Oliver's cash-for-guns event in the Glades, as well as Sebastian publicly taking a stand against the gunrunner The Mayor. Oliver encouraged Sebastian's run for Mayor of Starling City, a movement that quickly gained a large amount of followers in the Glades.
At the same time, Isabel Rochev, the Vice President of acquisitions at Stellmoor International, quickly attempted to take control of Queen Consolidated away from Oliver. She was partially successful, unable to completely force him out but relegating both of them to co-CEOs. Isabel quickly gained a favorable rapport with the board, as she was doing most of the work while Oliver (to the outside) seemed irresponsible with the company.
Additionally, Oliver and Isabel had a one-night stand while they were in Russia, leading to Oliver believing to have a bond with her. Unknown to him, just like Sebastian, Isabel was working with Slade due to her believing to be Robert Queen's soulmate to the point they were going to run away together, even though he left her to stay loyal to his family. His leaving drove her to vengeance against his family.
After many trials of the Mirakuru serum pulled from Slade's blood, including the failed trial of Max Stanton, Brother Blood found an acolyte able to handle the Mirakuru in Cyrus Gold, his former childhood preacher. Gold proceeded to pull off an impossible robbery with his newfound strength, stealing a centrifuge from Queen Consolidated.
The robbery caught the attention of both Oliver and Barry Allen, a forensic scientist from Central City, due to its impossible nature. The realization that one man had broken through the steel door and broke a man's neck with one hand made Oliver realize what they were dealing with and begin acting erratic.
Gold successfully pulled off multiple robberies, particularly stealing O-blood from a blood bank. Although the Arrow confronted him in his stolen truck, he managed to escape. Oliver confronted Gold one more time at an ARGUS bunker, but he was beaten to near death, only revived due to Barry's efforts.
Oliver and John Diggle attempted to confront Gold one more time but narrowly escaped. In an effort to take him down, the Arrow met with Quentin Lance and asked him to do it, but unknown to them both, Officer Daily, a member of the Church of Blood, joined the raid and warned Gold they were coming. In the following raid, all of the officers except for Lance and Daily were killed.
At the same time, Roy Harper and Thea Queen were recruited by Glades resident Sin to look into Max Stanton's death after the police (led by Officer Daily) ruled his death an OD. Roy tried to get The Arrow's help, but the red tear tracks on Max's body confirmed to Oliver that this was Mirakuru and he ordered Roy to stay out of it.
Undeterred, Roy broke into the scene of one of Sebastian's latest blood drives (the one that Max went to shortly before his death), but he was caught. He was brought before Sebastian and injected with the Mirakuru serum just before the Arrow intervened. The subsequent fight led to Gold's death, with Roy barely surviving and Brother Blood managing to escape.
Slade confronted Sebastian and told him that he will get more of Slade's blood this time, but that his mask could be worn by another if he fails again.
Investigating Sebastian Blood
Oliver attempted to find Brother Blood, but no one on the street was aware of his existence. He remained completely unaware that their civilian sides were good friends, as Oliver remained as a backer to Sebastian's campaign for mayor.
After Sebastian's unity rally to show defiance against the serial bomber Mark Scheffer, The Arrow offered his allegiance to Sebastian, with the two of them shaking hands in his office to showcase their alliance and shared goal.
The rally also showcased Roy's increased strength after he protected Moira from danger, leading to both Thea being suspicious and Oliver deciding to help him control the serum.
On a tip from Thea, Laurel Lance, who had begun seeing Sebastian, began looking into the possibility that he was Brother Blood. Confronting him in his office, Sebastian told a story of half-truths, confirming that he knew Cyrus as a child but that he was a good person that he hasn't seen since. After he stepped out, she took papers related to his mother, Maya Resik.
After visiting her in a mental hospital, Laurel realized that Sebastian killed his father before framing his mother for it. To cover his tracks, Sebastian visited his mother and scared her using his mask, causing a fatal heart attack and making her even more suspicious. With nowhere else to turn, Laurel contacted the Arrow for help.
Although Oliver was hesitant to believe that Sebastian, the man he publicly supported, could be more than he thinks, he believed Laurel and the two of them broke into the City Archives to find his files. However, the file was empty thanks to Slade having stolen it previously, and the two escaped empty-handed.
Laurel returned home only to find Officer Daily, who then arrested her for her drug abuse. Her previous behavior led to Quentin and Oliver both not believing her suspicions.
As a final way to clear his name, Sebastian had Laurel kidnapped. Oliver found her, but Laurel confronted and killed Brother Blood in the ensuing conflict. The two took off the mask, only to discover that Daily was under the mask and not Sebastian, making Laurel doubt herself as well. Unfortunately, her drug problem led Adam Donner to disbar her.
Moira for Mayor
After an incident where Roy almost killed someone with his increased strength, the Arrow finally confronted him and offered him a way to learn to control his strength and rage. With no other choice, Roy accepted, only to discover that he did not agree with the Arrow's methods.
In order to save the city from another earthquake generator, Oliver was forced to reveal his identity to Roy. The two forged a tentative partnership.
At the same time, Walter Steele and Thea managed to convince Moira to run for mayor, putting her in direct conflict with Sebastian, despite her worries of Thea's paternity becoming public. Oliver agreed to pull his support from Sebastian, who completely understood.
To prevent Thea's paternity from being released, she bribed Thea's doctor using Tempest's money, catching Felicity Smoak's attention and making her realize the truth of Thea's parentage. Despite Moira's threats, Felicity confessed the truth to Oliver, who then told Moira that "Privately, you and I are done".
At the same time, Sara Lance was released from the League of Assassins by Nyssa al Ghul, allowing her to publicly return home. Unfortunately, Laurel learned that Quentin had kept Sara's survival from her, causing her to lash out at everyone and alienate even Oliver. Oliver telling her he was done running after her finally led Laurel to get help.
Slade finally decided to take care of the Moira problem himself, arranging a meeting in her mansion posing as a political benefactor. Thea, who had previously realized that there was tension between her brother and mother, faked a 911 text to get Oliver to the mansion, where he then ran into Slade on his own and was shocked.
Although Oliver attempted to attack Slade while Moira was out of the room, Slade demonstrated that he still had the Mirakuru in his system. After convincing Thea to give him a tour of all of the artwork in the mansion, Oliver called Sara and left the phone on speaker so she would hear Slade's voice.
Sara mobilized the team; she had Roy promise to get Thea out of Slade's sight while she snuck into the house through the upstairs window. The plan was to have Diggle shoot Slade with the highest caliber weapon they could find when he left the mansion, so they armed him with a high caliber sniper rifle.
After Sara arrived, Roy got Thea away from Slade while Moira left on her own, leaving Slade and Oliver alone. Slade took the opportunity to mock Oliver and remind him about the promise he made on Lian Yu. Slade also took notice to the fact that Diggle had not shot him yet, making Oliver realize that he had been attacked. Unable to do anything to him, Oliver allowed Slade to leave.
Oliver, paranoid that Slade would kill everyone he loved, established guards for everyone in his life; he had Diggle increase security for Moira while he watched Felicity, while Roy guarded Thea and Sara guarded Laurel.
Oliver's paranoia gave him a single-minded drive to destroy Slade, leading him to contact the Bratva and fight Alexi Leonov's bodyguards to gain information. Alexi cut him out of the Bratva as a result, while Oliver did not care about the future problems he was creating by angering the mob.
With his presence known, Slade began to openly stalk Oliver, watching him from rooftops and leaving Deathstroke masks with an arrow in one eyehole to taunt him.
Using the Bratva's intel, Oliver went to Slade's hideout, only to discover Alexi dead with an arrow in his eye and old videos of Shado. Realizing he wouldn't be able to defeat Slade without help, he went to Amanda Waller to explain the situation, causing Amanda to realize Deathstroke's identity.
Gaining Queen Consolidated and an army
In order to protect Thea, Oliver ordered Roy to break up with her. Although it took a while to convince her, Roy eventually kissed another girl to get her to break things off. Devastated and alone, she wandered through the street that night, eventually getting picked up by Slade.
Thinking him to be friendly, Thea got in the car with him before he showed his true colors. Screaming at her to get out, Slade scared her enough for her to get out and run only to be intercepted and kidnapped by Brother Blood.
At Moira and Sebastian's debate the next night, Slade recorded a video of Thea begging for help to disrupt the debate. Both campaigns were put on hold to find her.
However, the annual Queen Consolidated board meeting could not be put off, so Oliver appointed Isabel as CEO temporarily to cover for him. Isabel took the opportunity to convince the board to give her full control, ousting Oliver from the company completely.
Felicity discovered a car registered in Slade's name, so the Team went to confront him. Oliver used Tibetan pit viper venom to knock him out before calling Quentin to arrest him. However, Slade was able to produce evidence that he had been in Costa Rica during Thea's kidnapping, exposing the Arrow's connection to Quentin as well as forcing the SCPD to let him walk free. Slade pretended to offer a monetary reward to anyone who helps find her to reporters before driving away.
Slade returned to where he was keeping Thea, telling her that she was free to go. Before she left, though, Slade told her that Malcolm Merlyn was her father, but twisted the truth to make it out as though Oliver knew about it for much longer than he did.
While Oliver and Moira managed to reconcile (at least partially), Oliver finally learned of Isabel's takeover of his company, also realizing that she worked for Slade. The two clashed in the CEO's office, only stopping when Isabel told him where Thea was supposedly being held and that he should come alone.
Oliver fought his way to Thea, but it was all a ruse constructed by Slade to put him somewhere else so that he could hijack an Iron Heights transfer bus. Slade quickly hijacked the bus and recruited the prisoners inside for his army.
Thea walked into the precinct unharmed, only to be hostile towards both Oliver and Moira due to the knowledge of her true father. Leaving the precinct, she didn't see Roy, who gave her one last look before leaving Starling City completely.
Thea's kidnapping caused Moira to move ahead of Sebastian in the polls, leading him to angrily confront Slade and Isabel. Slade brushed him off, but Isabel revealed that Queen Consolidated was ready to replicate the Mirakuru serum based on Slade's blood.
With no other choice, Lieutenant Pike was forced to arrest Quentin for working with the Arrow, eliminating Oliver's contact within the police.
In an effort to create another distraction for Oliver, Slade went to Laurel's apartment and confronted her. Stating that he was not there to harm her, Slade instead told her about Oliver's identity as the Arrow before leaving her alone.
On the defensive
Team Arrow took the fight to Slade by breaking into Queen Consolidated and blowing up the Applied Sciences division, stopping Isabel from replicating the serum. Oliver fully admitted that this was only a setback, but it was a start.
Unfortunately, Oliver could not regain control of the company, and without Thea's signature, they couldn't even protect their assets. With Thea alienated from her family, the odds were high that the Queens were going to lose everything.
Slade went back on the offensive by breaking into Team Arrow's lair underneath Verdant, fighting all of Team Arrow at once and winning. Not only did the victory mess with Oliver's head, but it also allowed him to steal the Clock King's skeleton key, giving him access to any lock in the city.
Using the skeleton key to break into the Starling City branch of STAR Labs, Deathstroke confronted Cisco Ramon and Caitlin Snow. Although the two managed to survive the encounter due to experimental weaponry found in the warehouse, Deathstroke found a biotransfuser and took it with his own two hands.
The team realized that Slade planned to use the biotransfuser to spread the Mirakuru in his blood to his soldiers to amplify all of them. With limited options, the team decided to wait for Slade to begin using it so that he would have no energy to fight back, allowing them to finally defeat him.
Oliver gave Isabel one more chance to do the right thing, only for Isabel to explain why she hated Oliver so much and make it clear she could not be redeemed. In her angry rant, she revealed that Robert was aware that Thea was not his daughter, prompting Oliver to attempt to explain the truth to her.
The combination of Slade talking to her and Sara being hospitalized led to Laurel finally accepting that Oliver was the Arrow just in time for her father to be hospitalized as well after being attacked in prison. Blackmailing Kate Spencer one more time, she managed to get him released with all charges dropped.
Oliver attempted to convince Thea to help save the family's assets, but at the same time, the biotransfuser went online. Left with no choice, Oliver went after the biotransfuser, only to discover that Roy was being forced to give his blood instead of Slade. Slade and Isabel arrived to gloat, and a fight broke out.
Although Diggle managed to shoot Isabel twice and Oliver managed to get Roy out, Slade still managed to revive Isabel with his own blood and finish the transfusion into the other inmates. The amount of blood that Roy lost was detrimental to his body and left him unconscious, but the Team couldn't take him to a hospital.
Using a sample of Mirakuru collected during the fight with Slade, Felicity asked Cisco and Caitlin to create a cure so they could stop Slade.
When Roy regained consciousness, he was nothing more than an animal acting on his basic instincts and attacked Diggle and Felicity, managing to escape. Team Arrow spent all night searching for him, but they couldn't find him.
Meanwhile, Moira's mayoral race was gaining traction over Sebastian's. Thea's dispute with Moira almost led to her canceling a rally she was holding at Verdant, leading to her realizing that she needed to be a mother, not a mayor, and deciding to drop out of the race at the rally.
After Sin contacted Sara, the team realized that Roy was at the Clock Tower and went to confront him. With his pure strength, Roy beat both Sara and Oliver and escaped, killing a cop as he fled. Hallucinating a vision of Thea telling him to kill her, he started heading towards Queen Mansion.
Thea learned that Roy was going crazy from the news and a conversation with Sin, leading to her deciding to get Roy's attention and try to get through to him.
Just before the rally, Oliver managed to get through to Moira that she shouldn't concede the race, leading to Moira continuing her campaign and angering Sebastian. Thea also took the opportunity to get in front of cameras and tell the city the rally was at Verdant, leading Roy directly to her.
Roy got the message and assaulted the rally, narrowly being beaten by Oliver, who used the Tibetan pit viper venom to knock him out. However, Sara, who had been vouching that Roy needed to die, realized that the darkness she tried to fight had never truly left her, sending her back to the League of Assassins to get back up.
As the three Queens were driving home, another car crashed into their limo. When Oliver woke, Thea and Moira were in front of him just like Sara and Shado were five years previously, with Slade offering him a similar choice: Moira or Thea. After Slade revealed that he and Oliver knew each other from the island, Slade screamed that he had to choose.
Moira made the choice for him by standing up and demanding that Slade take her and spare her children, against both of their pleas. Slade noted the courage she had before stabbing her in the chest, horrifying the other two, before leaving them in the woods as she died.
With Moira dead, Sebastian was sworn in as Mayor of Starling City. Isabel took the opportunity to reveal her survival to Diggle and Felicity at her funeral since Oliver himself had been too emotionally devastated to attend himself.
Desperate to stop Slade's plan, Diggle and Felicity went to Amanda Waller to ask her to locate Oliver, in the process revealing that Slade had an army of Mirakuru soldiers. Waller told the team where to find Oliver, but warned them that the situation needed to be contained or else she would have to act.
The two barely managed to convince Oliver to come back to the city. Even then, he decided to surrender himself to Slade in order to protect his family, begging Thea to flee the city so that she wouldn't see what happened to him. The brother and sister finally made up before Thea left.
Meanwhile, Laurel's suspicions about Sebastian were reignited due to the strange timing of Moira's death. Faking a meeting with him, she planted a bug in his office that allowed her to see all of his computer files. Although he was almost completely clean, she and Quentin discovered that the article he wrote regarding Moira's death was written before she actually died, leading them to realize Sebastian's identity as Brother Blood.
Oliver didn't listen to Diggle and Felicity's desperate pleas to save himself and instead went to deliver himself to Slade. Before he could, however, Laurel knocked him out and brought him back to the Arrowcave, revealing that she knew his identity and telling him about Sebastian when he woke up.
Reinvigorated by Laurel's trust in him, Oliver confronted Sebastian and revealed that he was aware of his partnership with Slade, as he is the Arrow. While Sebastian did not seem surprised, even commenting that it explained a lot, he gloated to Oliver that the city was his and that Slade would win.
At the same time, Diggle and Felicity interrogated Clinton Hogue, Blood's head of security, through threatening his personal finances until he told them all he knew. Although he didn't know the specifics of any plan, he told them whatever was happening was that night from within the sewer system.
The team chose to infiltrate the sewers and blow them up to collapse them on Slade's army, but the plan was unsuccessful. It also did not account for people Slade placed around the city; one attacked the police station after being brought in, while another began attacking civilians at the train station Thea was at.
Although the team survived, Laurel and Oliver were trapped underneath rubble while Diggle was confronted by a Mirakuru-empowered Isabel, leaving them unable to prevent Slade's Army from beginning a march on the city.
With Slade's army being superhumanly strong and resilient, chaos spread quickly within the city. Although Quentin and Malcolm Merlyn managed to dispatch the soldiers in the police station and train station, no one was able to stop the other soldiers from attacking the city, causing destruction, and killing civilians.
Meanwhile, Sebastian allowed the destruction to continue, remaining calm through the entire ordeal and refusing to call in the National Guard.
Laurel and Oliver managed to free themselves while Felicity ran Isabel over with a truck, allowing the four of them to get away. While Quentin begged Laurel to come back to the precinct, Felicity received a call from the STAR labs courier containing Cisco and Caitlin's cure saying he was in the city but that his car had been attacked.
Laurel split from the rest of the team, eventually making it back to the police station with her recently returned sister Sara/The Canary. At the police station, Lieutenant Pike revealed that Quentin knew the most about the situation due to his association with the Arrow and ordered him to lead the police efforts, promoting him to Detective to do so. Quentin contacted Oliver and told him that the police are complete with him and began orders for establishing a safe zone.
The rest of the team went after the courier by tracking his cell phone but were interrupted by a few soldiers who caused Diggle to crash the truck. While they were able to continue, they were unable to prevent another soldier from killing the courier and taking the Mirakuru cure after Slade heard about it through a bug on Felicity's phone.
After a soldier killed most of Sebastian's staff, including DA Spencer, he confronted Slade in Queen Consolidated about him honoring his promises, only to be rebuked by both Slade and Isabel. Realizing that the two people he was working with were insane and were willing to destroy Starling City completely over their grudges with Oliver, he stole the cure and contacted Oliver to give it to him.
After having Diggle retrieve Roy, still unconscious with Tibetan pit viper venom in Verdant's basement, Oliver confronted Sebastian. Although Sebastian seemed to have regrets and warned Oliver that whoever he loved the most would be the last to die, he still warned Oliver that if he told anyone about Sebastian's role in the Siege that he would reveal that he was the Arrow. Oliver took the cure and left.
Not long after, Isabel confronted Sebastian, who revealed that he stole the cure. On Slade's orders, Isabel stabbed Sebastian with her sword, with his dying words proclaiming his love for the city.
Team Arrow reunited in the Clock Tower with Roy's unconscious body and the cure in their possession. Oliver was hesitant to use Roy as a lab rat to see if the cure worked until Quentin called him to tell him that the army was establishing a perimeter. Realizing that “the army” was actually ARGUS, Oliver contacted Amanda Waller.
Waller revealed that she was forced to have a backup plan to prevent Slade's army from destroying the whole country and that she had not only established a perimeter but also had a drone ready to completely blow up the city should he fail to stop Slade's army. Oliver managed to convince her to postpone it to sunrise, but after that, Starling City would be destroyed.
With a strict time limit to save the city, Oliver gave Roy the cure. Although it didn't seem to work at first, Roy eventually woke up as Slade's soldiers attacked the Clock Tower. Roy attempted to punch a soldier, only to injure his hand, making the Team realize that the cure worked.
Although Slade's soldiers almost caught the team, they managed to escape with a line that Diggle attached to the opposite building just before Lyla Michaels arrived in a helicopter to completely destroy the Clock Tower, killing all of the soldiers inside.
The team returned to the Arrowcave, only to find it completely destroyed. They were then joined by members of the League of Assassins, particularly Nyssa and Sara. Sara, as it turns out, promised to return to the League in exchange for their aid in stopping Slade, something that Oliver hated but couldn't change.
The team and Assassins then raided Queen Consolidated, using the cure to disable all of the soldiers in their path. Although Slade managed to escape, Nyssa snapped Isabel's neck, killing her for good.
Another soldier then attacked the police station. Quentin was unable to stop him, leading to Laurel being kidnapped for the final phase of Slade's plan.
Quentin joined the team at Queen Consolidated, where they all realized that Slade's soldiers were gathering at one of the tunnels. Oliver took that as a challenge and ordered everyone to be ready. While Oliver was torn over whether or not to kill Slade, Quentin argued for it and Felicity argued against it.
Before confronting Slade's soldiers, Oliver took Felicity to his former mansion and told her to stay there. Although she tried to fight it, Oliver told her that she has to stay because Slade will kill the one he loves and that if Felicity died he wouldn't be able to take it.
This turned out to be a ruse; Oliver had discovered that Slade had bugged his mansion at his first visit and manipulated him to believe that he loved Felicity. Slade then kidnapped Felicity, unaware that Oliver had given her a vial of the cure.
Meanwhile, Diggle and Lyla went to ARGUS headquarters, breaking in and releasing Floyd Lawton from his cell. The three of them managed to take down all of the ARGUS operatives except for Waller herself, who taunted Diggle by telling him Lyla was pregnant.
Oliver, Roy, Sara, Nyssa, Quentin, and the League Assassins all converged on the tunnel and confronted Slade's forces. After an intense battle, Team Arrow came out on top, curing all of Slade's forces. Although Oliver attempted to convince Waller that she could call off the drone, she refused to back down until Slade himself was defeated.
Slade then called Oliver and taunted him, revealing that he not only had Laurel, the woman Slade thought he loved, but he also had Felicity, the woman Oliver had only just proclaimed his love for. Slade told Oliver to confront him or they would both die.
Oliver met him while he was holding a sword to Felicity's throat and asked him about Shado, specifically whether he remembered how kind and loving she was. While he distracted Slade, Felicity managed to sneakily stab Slade with the cure, ridding him of the Mirakuru.
The two then fought one more time, with Slade taunting Oliver by saying that the Mirakuru didn't make him hate Oliver or that he couldn't win unless Oliver killed him. However, their battle finally ended when Oliver used one of his trick arrows to tie Slade down. Oliver contacted Waller one final time telling her that Slade was defeated, causing her to retract the threat of blowing up the city and finally ending the Siege.
In an ironic twist of fate, Slade was incarcerated at the supermax prison on Lian Yu. Isabel and Sebastian's roles in the Siege were eventually revealed to the public.
Although the Siege was a failure, it had a large number of long term effects on the people that lived in the city. Not only was Anna Loring's death at the hands of one of Slade's soldiers the catalyst for Ray Palmer becoming the Atom, it also directly led to Carrie Cutter becoming Cupid after Oliver saved her life.
The Arrow's role in defending the city led to Quentin publicly recognizing him and thanking him for his help, beginning the partnership between Team Arrow and the SCPD. On the other hand, Alexi's death at what appeared to be Oliver's handled to his fallout with Anatoli, causing him to be ousted from the Bratva.
After Malcolm saved her life during the Siege, as well as after Roy lied to her to fight in the tunnel, Thea decided to leave Starling and travel with Malcolm to Corto Maltese. Malcolm used the opportunity to drug Thea and have her murder, Sara Lance, causing the chain of events that eventually led to the Outbreak.
Roy's guilt over killing a police officer while affected by the Mirakuru was one of the motivators for him taking the fall for the Arrow when the SCPD turned against him.
Oliver later referenced the Siege during the Genesis event to mention events the city had managed to survive and increase the citizen's hope.
After three years, the Mirakuru rage finally faded from Slade's mind, leaving him wracked with guilt for all of the destruction and death he caused. At Oliver's behest, he has begun working towards redeeming himself through his journey to find his sons Joe and Grant.