
Marvel's final Phase 5 movie has set the stage for a serious conflict between two major Avengers team members, which could lead to another rivalry like in Captain America: Civil War. The third Captain America movie saw a schism divide the superhero team as Iron Man and Captain America came into opposition over the Sokovia Accords. While this conflict was eventually resolved, the Avengers have been left in disarray since Avengers: Endgame, and the events of Thunderbolts* have laid the foundation for new drama within the team.
Thunderbolts* sees several MCU antiheroes form an unlikely team comprising Florence Pugh's Yelena Belova, Sebastian Stan's Bucky Barnes/Winter Soldier, David Harbour's Red Guardian, Wyatt Russell's U.S. Agent, and Hannah John-Kamen's Ghost. The movie, directed by Jake Schreier, is one of Marvel's highest-rated in Phase 5 and paves the way to a climactic sixth phase.
Thunderbolts* Sets Up Conflict Between Avengers Teams

Warning - This article contains spoilers for Marvel's Thunderbolts*.
The ending of Thunderbolts* establishes a new team of Avengers in town, and their formation seems to have caused a rift between two old friends.
After saving New York City from The Void (aka Lewis Pullman's Sentry), Valentina Allegra de Fontaine (Julia Louis-Dreyfus) proclaims the ragtag Thunderbolts team to be the new Avengers. The movie's credits then show the world's reaction to this news, with the media reports revealing mixed feelings the people of Earth have toward their new protectors.
The post-credits scene of Thunderbolts* reveals that it's not just the people who are unwelcoming of the new Avengers, but other heroes as well.
When the new Avengers return in their newly minted superhero suits to their new Watchtower, Yelena reminds the team that despite the public mistrust, they are the real Avengers, because "the government said so," before asking Bucky, "Why doesn't Sam Wilson understand that?" Bucky replies that Sam (Anthony Mackie) "does have the shield" indicating that the new Captain America is one of the decision-makers in this process.
Yelena questions what would happen if Sam assembled a team to rival theirs, wondering which team is "the real Avengers." She asks Bucky whether he had talked to Sam about it, given that the two are friends, and Bucky responds, "I already did... it went poorly."
This is surprising news given that the last audiences saw of Sam and Bucky, they were still close friends - a result of their shared bond with the original Captain America, Steve Rogers, and their battle for his legacy in The Falcon and the Winter Soldier. Bucky even supported Sam in his hour of need in Captain America: Brave New World, reminding his friend that Steve didn't make a mistake in choosing Sam to succeed him.
It appears Bucky's place on the New Avengers is enough to fracture his friendship with Sam, whom the President had tasked with re-starting the Avengers in Captain America 4. With the government now sanctioning Valentina's New Avengers team, and President Ross (Harrison Ford) imprisoned on the Raft, Sam may take matters into his own hands to solidify his Avengers lineup as the dominant one.
Is This The MCU's Civil War 2?

Marvel Studios has confirmed that Mackie, Stan, and the rest of the New Avengers actors will be involved in the next major crossover film, Avengers: Doomsday (see who else is a part of the cast here). While the heroes will be busy dealing with Robert Downey Jr.'s Victor von Doom, they may also be contending with rival Avengers teams.
As Yelena reveals in Thunderbolts' post-credits scene, Sam has not taken the arrival of the New Avengers lightly. She reveals that Sam "filed for copyright of the [Avengers] name," which has led to the New Avengers "losing credibility."
Until now, the MCU has stayed away from confirming who will be a part of the next Avengers team, and it appears that Avengers: Doomsday may have two competing for the title.
This could lead to another Civil War-esque situation in the MCU, where old friends Bucky and Sam turn against each other as they fight for their Avengers team to be considered the "real" one. However, it's unlikely that this conflict will last long, as the Avengers teams have shared troubles regarding the arrival of the Fantastic Four and Victor von Doom, which may force them to put their differences aside.