The US already had all the power when people called it the leader of the free world, when people start using the word "bully," that signifies a major shift.
But WW2 ended colonialism and 90s globalization spread industrialization worldwide, leaving us all in the slow roll of reverting to the mean now. At the end of which, the ancient civilizations of China and India, with nearly 3 billion people between them, will return to global dominance.