Hi guys! Before you start reading this, here's an explanation about what's going on. This series takes place in the alternative universe created by the Avengers when they traveled through time in order to grab the stones in Endgame. It may seem farfetched but it's the only explanation for the time travel to make sense (I actually wrote a thesis about alternative universes and time travel in fiction so I did my research). Besides, the Marvel multiverse was confirmed with the new trailer for Spiderman Far From Home so…
I haven't seen the older Marvel movies in a while, but here are the elements that I think could change in this chronology/universe because of Endgame (I probably forgot things, I'll add them as I remember them). Remember it's all speculations:
– Since OriginalSteve (let's call him that for clarity's sake) in Endgame goes back to Peggy (I'm guessing in the fifties?), she doesn't marry someone else (I'm not taking into account the theory that Steve was the mysterious husband for this universe) and doesn't have the two children she has in the original universe. Meanwhile Steve from that universe is still in the ice.
– In 2012 after the Battle of New York, because of Stark and Lang's interference, Loki escaped with the Tesseract.
– In 2013, Loki isn't in Asgard but I think Thor's story wouldn't really change in this film since he would be looking for Loki and I believe would eventually find him. So let's consider that the Ether was indeed brought to the Collector at the end of Thor 2 The Dark World. As for the Tesseract, let's say it stayed on Asgard. I'm unsure about Loki's whereabouts though.
– Since Thanos and his minions traveled in 2014 to 2023, the events of The Guardians of the Galaxy are completely different. Since Gamora's fate wasn't really clear at the end of Endgame, let's consider that she's alive (and hasn't been reduced to ashes like all of Thanos' army because she wasn't a part of it anymore) and that she's in the original universe (remember, the time travel can't change the past, so OriginalGamora remains dead). Basically, The Guardians of the Galaxy have been robbed of their Gamora before they even met.
– So since Gamora is gone and Nebula is dead (no grandfather paradox because it's a different universe, yay), things are different. Ronan can't make a deal with Thanos anymore and I think he would still attack Xandar but fail to pierce its defenses. So Xandar is safe.
– Because Gamora is gone, she doesn't attack Peter (let's consider that Steve put the Power Stone back on Morag and Quill just woke up and thought he slipped, knocking himself out) on Xandar but Rocket and Groot still do. Because of the mess they make, they are still sent to the Kyln prison.
– Because Gamora is gone, Drax doesn't attack her in the showers and doesn't make a deal with Quill. But Quill, Rocket and Groot would still manage to escape on their own I think.
– But because there is no Gamora, then they don't know about the Collector and his willingness to buy the stone so they don't head to Knowhere. Peter tries to escape because Rocket contacts Yondu for the bounty.
– From there it could go a lot of different ways, but let's consider here that Quill was delivered to Yondu, Rocket and Groot got paid and went their merry way. Quill then negotiated with Yondu because he has the stone. I think that Quill would be able to escape Yondu if he gave up the stone. I'm not sure he would go back to the Ravagers. Oh and the whole Guardians of the Galaxy Vol. 2 wouldn't happen.
– Since the main changes in this universe are the things related to the stones and how Thanos affected that, I don't think much of the rest would be changed. Of course, Avengers 3 Infinity War and Endgame wouldn't happen but other films like Captain America 2 The Winter Soldier, Avengers 2 Age of Ultron, Captain America 3 Civil War or Black Panther and Doctor Strange would still happen. (I'm still unclear about Thor 3 Ragnarok but maybe one of the fics in this series will deal with that because Hela is too great a villain to not have her make one hell of an appearance).
So basically, what needs to be remembered in this universe is that: Loki is alive, Nebula is dead, Thanos and all his minions are dead (including the Black Order and Korath), Gamora is gone from 2014 onwards, The Guardians of the Galaxy were never formed, Vision was made and is alive, Tony is alive, Steve is alive, Natasha is alive. Also, most of the stories in this universe will take place after 2016, after Civil War happened with a new wave of Avengers led by Cap and Widow. I really liked some of the developments of Endgame, therefore somewhere around 2017-18 in this universe Morgan Stark will be born. Also, Peter Parker will join the Avengers around that time.