Finally, an explanation for U.S. policy

I knew there must be an answer for the often-nasty behavior of the U.S. The Onion to the rescue:

"In its adulthood, the U.S. displays all the classic tendencies of a nation that was repeatedly mistreated in its infancy—difficulty forming lasting foreign relationships, viewing everyone as a potential enemy, and employing a pattern of assault and intimidation to assert its power," said Dr. Howard Drexel, the report's lead author. "Because of trust issues stemming from the abuse, America has become withdrawn, has not made an ally in years, and often resents the few nations that are willing to lend support—most countries outgrow this kind of behavior after 230 years." More.