How was the united states needed to the countries that were destroyed?

By the end of World War II, much of Europe and Asia, and parts of Africa, lay in ruins. Combat and bombing had flattened cities and towns, destroyed bridges and railroads, and scorched the countryside. The war had also taken a staggering toll in both military and civilian lives. 

Shortages of food, fuel, and all kinds of consumer products persisted and in many cases worsened after peace was declared. War-ravaged Europe and Japan could not produce enough goods for their own people, much less for export. 

What was needed to pull Europe and Asia back into the international economy? The answer was money - but what kind? The currencies of war-torn countries? Gold? Dollars?