The British pound was displaced by the US dollar. Currently, the US dollar just doesn't have a proper rival. The euro, yuan and rupee are considered politically suspect (each for its own unique reasons); the pound and yen have too small a base. Without further transformation of the global financial system, the only alternative is for banks to hold a basket of currencies, and in such a basket the dollar would likely still play a significant, if reduced, role. This is a slow process because it means changing the nature of currency reserves from a single safe haven to a "nest". What this means for USG spending power is not immediately clear.