The end of the American empire is determined by the fact that the USA won't be able to pay for the expenses of maintaining its military force. The US is already wasting more than half of its discretionary spending on the military. These military expenses already account for 89% of the federal government deficit, which will be $1.101T in 2020 [1]. These expenses are going up faster than GDP growth, and are not expected to go down, since this administration refuses to close the 20-years old wars on Afghanistan and Iraq, and is now actively operating in other fronts of the general war on the Middle East. The US also has to maintain more than 800 military basis in 70 countries. It takes huge amounts of money to keep a military force of this kind, especially when the country is under severe deficits, which is the current situation of the US government. It seems that it will take a few years for the shoe finally drop, but all the bravado of the Trump era is moving the US into a situation in which it cannot afford to maintain its empire.

[1] https://www.thebalance.com/u-s-federal-budget-breakdown-3305...