[quote=@KabenSaal]
Yea. You don't invade planets without having a plan. That's why they're called planets, to remind you to plan it. 

But more, our side. You don't send your entire planet to invade someone, which means this is just the occupation force. We are going to have to invade them in response or they will just send another army.
[/quote]

Maybe you're granting these aliens too much scope. It could be that this is a small, aggressive alien nation who mistakenly believes it has the necessary tech to take over the "inferior" human species. Perhaps they don't and/or cannot muster another invasion force. Invasion does not necessarily mean there will be more if the first wave is defeated.

Especially if we decimate them and send their heads back to their commanders on skewers.