What factors led to the economic prosperity of the postwar era?

The G.I. Bill was a major factor, providing education for returning servicemen and providing a more educated workforce.  

The ramping up of wartime productivity in United States manufacturing was turned toward manufacturing of consumer products.  President Truman delivered a special message to Congress in 1945 urging the facilitation of this conversion of industries to peacetime purposes.   Both President Truman and President Eisenhower worked to reduce government expenses for the sake of the nation's economy.

The Eisenhower administration also boosted economic advancement by investing in infrastructure, notably the building of interstate highways for commerce.