Timing will be crucial. The economic collapse of the US may trigger a similar collapse of China … but only by preceding it. Which of them is better prepared to go to protracted war? Who has the most steel mills, working factories (making clothing, boots, ammo), capacity to expand quickly? Which has the most determined political leadership? Which of them has mousetrapped its military with a thousand politically correct “Mother, may I” rules? How many of such self-imposed disadvantages are outweighed by putatively superior technology?
Remember that when FDR engineered the attack on Pearl Harbor, to make a way to go to war with Germany, that we were a self-impoverished nation, just climbing out of the Great Depression, and Germany was well armed, and (until it got itself bogged down in Russia) newly prosperous, thanks, in great part, to copious financing by certain British and US banks. It took a lot of doing (and “borrowing”) to get the US up to its manufacturing potential. If the present day US trips first, especially if the result is armed secession movements, might not a militarily prepared nation (China? Russia? a partnership?) see opportunities for quick solutions to its foreign challenges?