This is a very misinformed commentary.
You are forgetting about the US Afghan and Iraqi allies who have been subjected to much greater horrors, as have Germany and Japan in the past.
And the US alliance with countries like India is too new to have been tested yet....wait till you have a problem with US and then see how you fare after that.
Starfor's George Friedman argues on page 28 of his book "The Next 100 Years" that "psychologically, the United States is a bizarre mixture of overconfidence and insecurity". This, he says, "is exactly the American condition in the twenty-first century. The world's leading power is having an extended adolescent identity crisis, complete with incredible new strength and irrational mood swings".
There are three stages of development of cultures: Barbarism, civilization and decadence, according to Friedman. He puts the United States currently in the barbaric stage. He says that "America, like Europe in sixteenth century, is still barbaric (a description, not a moral judgment). Its culture is unformed. Its will is powerful. Its emotions drive it in different and contradictory directions".
Haq's Musings: Is America Young and Barbaric?