As the 21st century drew to a close in the 1990s, the Avengers went through some major changes. For starters, Thanos set in motion an intergalactic conflict for the Infinity Gauntlet. This was followed by several other large-scale battles involving alien races like the Skrulls.
If this wasn't enough, the Avengers went through several internal conflicts too particularly between Iron Man and Captain America. All in all, this was an action-heavy decade for the 'Earth's mightiest heroes' as they battled one threat after the other.
Operation: Galactic Storm (Crossover)
As the Kree and Shi'ar races are involved in an interstellar war, the Avengers have no option but to intervene. But it's the behind-the-scenes drama of this conflict that makes the story all the more interesting.
While Captain America and Iron Man have had many team-ups earlier, the two Avengers leaders have been at loggerheads at times. Similarly, in Operation: Galactic Storm, when Iron Man and a few peers agree to kill a Kree leader, Captain America actively protests against the idea. Such fights over morals and ethics show how diverse the team is as a whole.
Avengers Forever (Limited Series)
The central battle in Avengers Forever spans several timelines spanning from the Old West to the future. As the Avengers vow to save their ally Rick Jones from a Time Master, the heroes unearth a larger mystery. Such is their situation that they decide to even join hands with their adversary Kang The Conqueror.
Even though Rick Jones was initially just a human, he got caught up in such interstellar conspiracies. Avengers Forever is easily one of the best examples to explain his importance in the larger continuity of the Marvel universe.
Ultron Unlimited (Avengers Vol 3 #19-22)
Ultron Unlimited is one of the most fleshed-out stories to understand the mechanical foe's origins. Ultron is revealed to be a creation of Hank Pym's (instead of Tony Stark as other comics claim). In this comic, Ultron gains such immense powers for world invasion that he ends up controlling the entire world's media along with destroying an Eastern European nation.
For those who are interested in knowing about Ultron and his powerful variants, this story arc makes for essential reading. The Avengers struggle to put up a fight against the villain while Pym is riddled with guilt for creating him in the first place. The takeover of Sloreina also adds an unexpectedly dark dimension to Ultron's menacing persona.
Heroes Reborn (Crossover)
In an alternate dimension, the Avengers have died and underwent a rebirth. This leads to a new set of Avengers that look and act differently. The characters receive new origins as the Fantastic Four overlooks this alternate Marvel history. Wakanda is just a myth. Captain America never froze in the ice. Iron Man never built an armor suit.
In other words, Heroes Reborn is a major 'What If' moment for the Avengers. It is a bold attempt by Marvel to rework some of its major heroes and villains. This eventually leads to the possibility of many other scenarios within a larger multiverse. The Avengers designs by top comic artists Jim Lee and Rob Liefeld serve as an added bonus.
Avengers: Death Trap, The Vault (Marvel Graphic Novel #68)
As Venom triggers a riot at the superhuman prison known as The Vault, the Avengers along with Freedom Force must stop the troublemaking assailants. But little do they know that Venom has deliberately created the situation as a trap for the heroes.
The one-shot is a straightforward story that captures the action-heavy storylines of Avengers comics in the 1990s. The addition of classic Spider-Man comic villains like Venom, Electro, Rhino, and others provides some freshness to the Avengers lineup of bad guys.
Bloodties (Crossover)
A major crossover between X-Men and the Avengers, Bloodties covers a civil war between the mutant and human inhabitants of Genosha. Magneto's former protege Fabian Cortez orchestrates the chaos and kidnaps Quicksilver's and Crystal's daughter Luna. As Quicksilver retains ties with X-Men and Crystal is an Avenger, both superhero teams get involved in the Genoshan conflict.
The storyline had far-reaching consequences for the Marvel Universe as it lead to the breakup of the Avengers team roster called West Coast Avengers (followed by the creation of Force Works). Following the events of Genosha, the Avengers themselves stopped operating under the mandate of the United Nations.
The Infinity Gauntlet (Limited Series)
After the nihilist warlord Thanos gathers all the Infinity Stones for his gauntlet, he becomes a god-like figure. With a single snap, he manages to wipe out half of the living creatures of the universe. Adam Warlock gathers the last of the Avengers to fight Thanos as he seeks the affection of Mistress Death.
The comic along with its sequels The Infinity War and The Infinity Crusade went on to influence several Marvel storylines and of course, the entirety of the Marvel Cinematic Universe. Even though writer Jim Starlin created Thanos way back in 1973, it is the six-issue Infinity Gauntlet that turned him into a formidable villain.
The Avengers: United They Stand (Tie-In)
A unique and short-lived adaptation of the Avengers saga was the '90s superhero cartoon United They Stand. Instead of focusing on the usual heroes like Captain America, Thor, and Iron Man, the show features Ant-Man, Wonder Man, Tigra, and others as the main members.
A tie-in comic series was set in the same continuity featuring the heroes in never-seen-before avatars. For instance, Hawkeye is prominently seen wearing armor that uses Pym Particles. Much like its source material, the comic lasted for only seven issues, but it still makes for an interesting and rare time capsule. Despite lesser popularity, the comic attempted at looking at the Avengers in a new light.
The Infinity War (Limited Series)
By the end of The Infinity Gauntlet, Adam Warlock seizes the Gauntlet. However, unlike Thanos and his grandaughter Nebula, Warlock wants to rationally use the Gauntlet to restore balance in the universe. And so, he ends up removing both of his good and evil aspects. But when this results in the return of his evil persona Magus, chaos ensues.
The Infinity War's protagonist might be Warlock, but several members of the Avengers and the X-Men make significant appearances. In fact, there comes a moment when Magus even creates evil doppelgangers of these heroes raising the stakes of the titular war.
Day-Break (Force Works #1)
Day-Break marks the first appearance of Force Works, a team born out of the remnants of West Coast Avengers. The titular team of the series includes Iron Man, Scarlet Witch, Spider-Woman, and Wonder Man. Tony Stark leads the team after breaking away from the Avengers due to ideological differences. As a member of Force Works, he and his team wish to prevent natural and human disasters even before they happen.
The very fact that Iron Man is willing to give up his status on the Avengers for a new team shows how even the greatest of heroes can grow exhausted. In the years to come, he would continue to have clashes, as is evident from comics like Civil War.