It seems long to us, but U.S. dominance has been perhaps 50-60 years, maybe a little longer. And it has not been so smooth during that time. Not very long compared to the British, or Spanish, or Roman, or Egyptian, or various Chinese empires. And now it is much more unstable.
Capitalism continues to have instability.
So that when there was a retreat, there was a tendency to go from extreme optimism to extreme pessimism. There are six billion people on Earth.