Did you read the marvel comics when worlds where colliding and they finally had the apocalypse between 'Ultimate universe' and the 'common universe' ? I think it was 'earth 616 and 1610 ... but I digress.
It's a choice, our world or another world crashing into our existence, think of a Newton's Cradle where all balls are tied to the same central point, and normally they all maintain a specific coordinate, but occasionally one gets misaligned. You want to save your world, they want to save theirs. This is the crux of the story IMO. Keep in mind this isn't THE ONLY TIME Waves have happened, its happened numerous times in the past as well.