u/Shadow_Senpai17

In the first trailer for Avengers: Doomsday, Doom warns that something is coming and that they must act quickly and take an unthinkable decision before it's too late, clearly setting up an incursion.

The real question is: an incursion between which Earths? We already know the X-Men are aware of incursions and are actively destroying other realities to save their own

We can deduce Doom warns Reed about an incursion between all 3 Earths (X-Men, 616 and F4), they reach 616 and warn their heroes about it, then they left for X-Men universe, these mutants are already traumatized by mass murdering and think these guys are here to destroy their earth so they start fighting before Doom's real plan get exposed

I don't think the movie is going beyond these three main universes, [possible leaked plot spoiler]>! though Tobey's universe is a possibility in the opening act if the leaks are true!<. Of course, if the trailer is only showing us the first act of the film, who knows how big it gets?

3rd one was terrible, hoping they will fix it

All these guys have somehow cheated death or changed their destinies.

The Loki series clarified that the Avengers going back in time was always meant to happen, so I’m not counting that one but you can if you want.

Maybe Doom is jealous. He lost everything, while these guys keep messing with timelines and changing their destinies for their own benefit without facing any real consequences. Or maybe their actions somehow triggered the events that ultimately caused Doom to lose his “everything"

maybe he lost his family in some event but he accepted it, he had great powers but he decided to accept it but then finds steve in his universe who cheated his destiny

though i trust Spider-Man, he is our hero but still concerning to handle crimes with help of Punisher