So what's new in the world, ramjam? Throught history countries of all ilks have allied themselves with other countries or groups which later become their enemies (or who were previously their enemies, or who were their enemies and who later become their enemies - all permutations in fact).
As for resentment, well it's always been easy for manipulative leaders to whip up hatred of the rich and powerful amongst those who feel deprived. Don't see many of those leaders strapping bombs to themselves though. Not likely!! Leave that to their brain-washed followers.
Like most countries, US foreign policy has a heavy dose of self-interest, but one might also reflect on their altruism which leads them to pump out a massive amount of aid and to interfere (maybe sometimes unwisely) against tyrannical regimes at some cost to their own people.
jon