Siege is the culmination of numerous arcs that began all the way back in Avengers Disassembled and continuing through Civil War, Secret Invasion, and Dark Reign. It begins where Dark Reign left off, with Norman Osborn tightening his stranglehold on the U.S. superhuman and intelligence communities. In an effort to consolidate his power further, he decides to take out Asgard, which is currently hovering over Broxton, Oklahoma.
The U.S. Government isn't on board with a full-scale invasion of Asgard, so Osborn decides to manufacture an inciting incident to get the public behind his plan. With the help of Loki, he manipulates the Asgardian god Volstagg into a battle with the powerful villains the U-Foes, which results in a massive explosion in a crowded stadium in Chicago. As Osborn prepares for a "pre-emptive" strike against Asgard, Marvel's heroes prepare themselves to stop his reign once and for all.
10 Ares Makes Osborn A Promise
When Osborn first Dark Avengers member Ares with his plan to invade Asgard, the god of war refuses out of his respect for Thor. To convince Ares, Osborn claims that Thor has been banished from Asgard and that Loki has imprisoned Odin and crowned himself the new All-Father.
Ares agrees to join Osborn's invasion but makes him a promise. If he learns Osborn has lied to him, he will kill him for his betrayal.
9 The First Wave
The first wave of Osborn's invasion of Asgard is a spectacular sequence. The Dark Avengers, Thunderbolts, Camp HAMMER trainees, and hundreds of HAMMER agents begin their assault on the floating city, with the Sentry breaking through its magical defenses.
Fandral the Dashing, of the Warriors Three, leads a force of Asgardians to meet their foes at the front gates. The gods find themselves outnumbered and overpowered by Osborn's forces, and hope seems lost until the timely arrival of Thor.
8 The Death of Ares
Thor's presence shocks Ares, who realizes that Osborn has, in fact, lied to him and made him a party to the madness unfolding around him. Across the battlefield, he shouts to Osborn that he is going to make good on his promise and kill him.
Before he can, the Sentry swoops down and engages the god of war in a massive brawl. While Ares manages to hold his own at first, the Sentry carries him into the sky and to the horror of everyone around them, tears him in two.
7 Captain America Returns
With everyone reeling from Ares' graphic death, it seems like Osborn has finally triumphed. That's when a familiar red, white, and blue shield soars through the air and smacks him right in the face. Captain America, thought by the world to have died at the climax of "Civil War," has returned and brought some friends with him.
Cap is followed by the Avengers, the Secret Warriors, the Young Avengers, and members of the Initiative, turning the tide of battle. Standing side-by-side for the first time in years with Iron Man and Thor, Cap has almost saved the day.
6 Thunderbolts Mutiny
Before the start of the Siege event, the Thunderbolts watched their leader Osborn mentally unravel more and more. Several members, including Paladin, Ghost, and Ant-Man (Eric O'Grady) have privately discussed when to best make their escape from under Osborn's thumb, as they are no longer able to stomach the amoral missions the madman sends them on.
When they are tasked with infiltrating Asgard before the invasion starts and steal the legendary Spear of Odin, their concerns finally come to ahead. Ghost alerts the Mighty Avengers to their presence in Asgard, and Paladin and Ant-Man battle their squad leader Scourge (a disguised Nuke) and teammate Grizzly. They escape with the Spear and head their separate ways.
5 Norman Osborn Shows His True Face
During the battle, Osborn's Iron Patriot helmet is broken. Crumbling to the ground he explodes into a full-fledged breakdown revealing a startling addition to his costume. He has painted his face green in order to crudely resemble his former alter ego the Green Goblin.
He rants and raves at the heroes around him, telling them that now that they have stopped him that he can no longer rein in the Sentry's darker impulses. He is then silenced by a quick punch from an annoyed Spider-Man.
4 Taskmaster Taunts Osborn
Taskmaster has always been a pragmatic mercenary. As the head of Camp HAMMER (the rebranded Initiative training center Camp Hammond) and a new member of Osborn's Cabal, he finds himself at the center of the battle. After being threatened and put down by Osborn over several weeks, he's already been having his doubts about his place in this conflict. Seeing the tide of battle has turned against his side, makes him decide to get out of Dodge while the getting is good.
Before he does though, he can't help tossing a barb at his old boss. While the Avengers have Osborn surrounded, Taskmaster calls out to him and lets him know that he had helped Deadpool blackmail him several months earlier.
3 Volstagg Triumphant
Osborn was right about one thing: with him out of commission the Sentry goes beserk. Poor Robert Reynolds gives way to his dark alternate persona the Void, reigning death and destruction down from the sky.
As the heroes are reeling from this development, Osborn makes a break for it. He manages to escape a little way before he is flattened (for the third time in this event) by Volstagg the Voluminous, the Asgardian he had used to begin his false-flag operation against the Gods. It's a sweet bit of justice delivered by a character often used as a comic relief.
2 Thor vs. The Void
With Osborn down for the count, Thor engages the Void in battle. It's an apocalyptic fight, with the most powerful Avenger going head-to-head with a being of total destruction. While he and the rest of the heroes are overpowered, Loki sees the horror all around him and prays to his father Odin for help.
The Void kills Loki, but Odin grants him his wish and gives the heroes a magical boost. Thor strikes down the Void, who reverts back to his human form. He begs Thor to kill him in order to prevent the Void from ever returning. Thor hesitantly agrees and calls down a bolt of lightning that practically disintegrates him.
1 The Heroic Age Begins
The entire world's discovery of Osborn's madness and illegal strike against Asgard leads to the U.S. Government dismantling HAMMER. Seeing the return of Captain America and Thor, public opinion also turns wildly in favor of the heroes, and the repeal of the Superhuman Registration Act and the Fifty States Initiative.
The President appoints Steve Rogers as the new head of SHIELD. Now America's "Top Cop," Rogers decides to lead the superhuman community into a brave new future. The Avengers have reassembled, and the Heroic Age begins.