Any if you are going to play with the words just use the extraterrestrial one.
But if they are traveling around, our own history suggests they're (probably) not peaceful. Then again, we have travelers who are traders, who are migrating, who are explorers, who are tourists etc. To travel doesn't necessarily mean you're expansionist; it's just that whenever you think of conquers, they were travelers - of course. You can't stay at home and conquer.
There's an interesting idea that to be conquered doesn't necessarily mean that your civic organization and culture is conquered. If your government etc works well, conquerers have often adopted it (ie they are conquered), and the rulers rotate, coup d'état. Military superiority doesn't necessarily imply civic superiority.
BTW: Headlines with puns or allusions are usually deliberate.