These countries – allies, strategic competitors, and potential foes alike – probably acted the way they did because they saw the downside of a world devoid of American power. For the allies, the calculus is simple: America guarantees their security.
For India, America provides a hedge against Chinese power. For China, an America-less Asia would bring to the surface latent but lethal rivalries among Japan, North Korea, South Korea, Taiwan, and China that could engulf Asia in war.
As for Russia, the demise of America would leave it alone facing a 1.3 billion-strong Chinese nation potentially eager to settle the empty former Chinese lands in the Russian Far East. America is uniquely valued as a market, a source of technology, and a place to educate elites.