National patriotism is easy to inspire when you have a powerful enemy attacking your shores and another attacking your friends. Less so today when the U.S. population is far more diversified and the enemy is an unidentifiable terrorist (until caught) attacking a single plane or a few buildings at a time in the homeland, and succeeding at that only every few years.
The recent car bomb attempt in New York City is an example. The attempt failed and most New Yorkers continue to go about their business like nothing happened. Today's war is vastly different than it was for Americans in WW II. In WW II, the enemies were nations and the soldiers wore uniforms. Not so today.