You could say that we experienced an almost 75-year stretch of triumphalism - think of it as the real "American Century" - from World War I to the end of the Cold War, with time off for a destructive stalemate in Korea and a defeat in Vietnam too shocking to absorb or shake off.
When the Soviet Union disintegrated in 1991, it all seemed so obvious. Fate had clearly dealt Washington a royal flush. It was victory with a capital V. The United States was, after all, the last standing superpower, after centuries of unceasing great power rivalries on the planet. It had a military beyond compare and no enemy, hardly a "rogue state", on the horizon.