The question of whether America is in decline cannot be answered yes or no. There is no yes or no. Both answers are wrong, because the assumption that somehow there exists some predetermined inevitable trajectory, the result of uncontrollable external forces, is wrong. Nothing is inevitable. Nothing is written. For America today, decline is not a condition. Decline is a choice. Two decades into the unipolar world that came about with the fall of the Soviet Union, America is in the position of deciding whether to abdicate or retain its dominance. Decline--or continued ascendancy--is in our hands.
Not that decline is always a choice. Britain's decline after World War II was foretold, as indeed was that of Europe, which had been the dominant global force of the preceding centuries. The civilizational suicide that was the two world wars, and the consequent physical and psychological exhaustion, made continued dominance impossible and decline inevitable.
-Charles Krauthammer, Things That Matter: Three Decades of Passions, Pastimes and Politics