Oooh you'd think. But nope, the Conquista didn't do wonders for Amerindian cooperation. In fact, each warring tribe, used to maximize complex alliance networks against their opponents, tried to benefit from the arrival of Europeans and use them to gain the upper hand in their own conflicts. Those who tried to unite against the threat had just no chance in front of short-sighted opportunistic politics. Also, outside (or inside) enemies are never a true factor of unification, the fake/artificial ones are always used to crush or demonize inner dissent by simply intensifying local antagonisms, and the true ones are always seen as opportunities to gain power upon the peers. Heck, we're currently facing global extinction threats by global enemies : global warming, pandemics, etc. How's our common front going ?
So much for the
green smurf strategy.
If anything, aliens would just have to stand back and watch
Maple Street burn...