The fact that the action of the picture, in accordance with the comics, the original source will occur not only in the present - where the team of Charles Xavier confronts the terrorists from the Brotherhood of Mutants (Brotherhood of Evil Mutants), but in the future - where the United States are groaning under the iron heel Guardians (Sentinels), a mutant herded into concentration camps. In the story of comics, Kitty Pryde from the future brings your mind into your body in the past and tries to warn there the X-Men of the terrible consequences that would come if not to prevent the assassination of Senator Robert Kelly. Then there are spoilers.
The idea of a producer (and director of the first two X-films) Bryan Singer (Bryan Singer) is to use the existence of parallel worlds, combine the old movie trilogy, "First Class" and "Wolverine: Origins", explaining all the trite inconsistencies branching time. Something similar happened to crank in "Star Trek" JJ Abrams.