The most ostensibly rich and powerful empires have gone bankrupt and collapsed. From Jeff Thomas at internationalman.com:
In 1944, the US had been the primary supplier for arms for the allies during World War II and, as such, exited the war with more wealth than any of the other nations that had entered the war earlier, draining their treasuries of money. Since payment was largely demanded in gold, the US held three-quarters of the world’s gold and therefore was in a position to call the shots with regard to the free world’s economic future.
At Bretton Woods, the US took advantage of this situation, setting up the World Bank and the IMF and declaring the dollar to be the default currency for all countries concerned. From that point on, the US was in the catbird seat, able to dictate economic terms to other countries and even to behave irresponsibly, eventually creating previously unheard-of levels of debt, thereby inspiring other nations to do their best to create their own debt in order to keep pace as best they could.
Eventually, of course, such irresponsible economics will cause any country, no matter how powerful, to collapse economically, no matter how many Keynesian economists such as Thomas Piketty, Paul Krugman, and Larry Summers declare otherwise.
Beginning in 1944, the US became the world’s foremost empire, for the strongest of reasons—it held the world’s wealth. This advantage led to a period of great power and, in the latter years, as the empire began to stumble economically under its own great weight, led to the creation of organisations and legislation designed to bring in new revenue, as the old forms of revenue declined.