If the USA wasn't starting and fighting wars it began without provocation , maybe there'd be less groups interested in "going there".

Besides, of the countries the USA considers an enemy, only Russia can ever "realistically" invade 'murica, and that's assuming they only focus on Alaska. Even if USA only had 1/3 of its current military, it'd send the Russians packing due to logistical advantage.

The only other route for Russia, China or anyone to invade is to use Cuba as a staging ground, which is not only very susceptible to a naval blockade, it's also within range of fuckloads of USA missiles.