The bad habit with which the United States was left by victory in the Cold War was to believe that the war had been a-zero sum game, which is to say that whoever won, won. They were now and forever Number One, the leader in whatever international situation demanded solution.
Islamic State? Stand aside — the U.S. will send bombers and lead a coalition. Ebola? U.S. special forces and military hospitals are on the way!
These don't in fact solve the problems, either the Islamic State or Ebola, or the rise in Taliban activity in Afghanistan or car-bombings in Baghdad, but all of this contributes to the American self-image as the "indispensible" nation — as U.S. Secretary of State Madeleine Albright put it in 1998, a phrase to be recalled and reasserted ever since.