The point was living off resources, it came down to your army again, invading... Then you couldn't support that so you had to resort to blowing up the countries... Which would just leave you to die anyway... So your army isn't saving you.
Dude, you do realize that you can take over/blow up a country without destroying everything in it...right. It is still possible to harvest crops in a country that is no longer run by its previous owners.
Oh and who's gonna explore the whole country to find uninhabited farms that still have undamaged crops, then harvest them and bring them back to the US and hand it out to people?
Lolk.