In last year's [X-Men: Days Of Future Past](tag:203942) we saw the X-Men attempt to wipe the Sentinels from existence by going back in time. Successfully doing so created a new reality and changed everything we know about their history, while simultaneously erasing the events of the original three X-Men movies.
Things did seem to change for the better, but tampering with something like time will obviously have its consequences, and what if Apocalypse is that consequence.
Director Bryan Singer posted a picture of Scott Summers parents watching the apparent end of the world on television. Meaning whatever Apocalypse has in store for us, it's definitely bigger than anything we've ever seen before and it's obviously going to change history further.
Besides in the Days of Future Past post credits scene, we did see that Apocalypse was viewed as a God like figure, meaning his presence and abilities clearly have a strong impact on humanity, however none of the original X men movies ever hinted at Apocalypse's presence. Which could mean that he wasn't around in the original timeline!
So what if Apocalypse was never meant to exist? What if he's the result of creating an alternate reality? That would mean that the X men themselves are indirectly responsible for creating their own doom.