By invoking the act, the United States could abstain from participating directly in a foreign conflict.
This is a very complex question, but they both collapsed due to:
decentralization and government corruption
plagues/ epidemics
high taxes
and invasions
Some differences are that the Chinese empires saw a revival while Rome didn't.
There were four major consequences of Second World War on India and they included high inflation which was on account of war expenditure, the value of Indian currency took a nose dive, economic imbalances due to currencies exchange problems and the development of exchange control. Lmk if this helps :)