Well, they didn't exactly come to conquer. If you follow the backstory, they destruction of earth was kind of a mistake. They had a big war over it, cause you know, it was the destruction of earth, but part of the whole idea is that the Votans didn't come to conquer - they tried to coexist first.

So now they're giving it a second shot. I kinda like it. It's a fresh take on the whole alien occupation thing.