Before the Incredible Hulk decided to quit the Avengers, the group is approached by man called the Scarlet Centurion, who claims to be from the future. He tells the Avengers that they will save the Earth if they remain together. So Hulk decides to stay. Centurion reveals them that in the future, a proliferation of superheroes will mean the planet's downfall. To prevent this, the Avengers should terminate every super powered being, villain or not.
The Avengers go on to defeat all heroes and villains. Unknown to them, they are under the influence of a Centurion's will-sapping ray. The Centurion was in fact Rama-Tut, a time traveling villain (who was at some point defeated by the Fantastic Four). Rama-Tut improved his will-sapping ray and planned his revenge by returning to the moment the original Avengers united. This time jump created an alternate timeline.
When the Avengers finish defeating all super powered beings, they announce that anyone else with super powers should report to the Avengers. Finally, the only super powered beings remaining in the planet were the Avengers themselves. The Hulk tries to leave the group but gets attacked by his peers. Iron-Man triggers the Hulk's transformation, and Bruce Banner is taken under the Centurion's custody. The remaining four disband: Thor went back to Asgard, and Iron-Man, Giant Man and the Wasp simply retired.
A few months pass, and the Scarlet Centurion announces to the world that he is their new leader. Any opposing force would be destroyed. The former Avengers (but without the Hulk) gather once more, and are able to defeat the Centurion.
Iron-Man asks the rest to stay in the group, but they decline, fearful due to their evil actions under the Centurion's influence.