The end of World War 2 is when we can look back and say that "this is the time period in which the age of Consumerism began." If this really was true, why was it companies that sold goods continued to operate and produce them within the United States? What prevented them from moving their factories overseas in the fifties instead of 40-50 years later? Was it tariffs? Was it trade restrictions? Would nationalism and pride in American-made goods have played a part? What was it?
Containerization.
Before the standardization of shipping, it was always more economical to produce goods as close to the destination as possible. The concept of containerization began to be explored in the early 20th century but it didn't take off until after WWII. The modern container was invented in 1955, and worldwide standards were not put into place until 1968. After containers became the dominant transportation method, shipping costs were reduced to the point that it became more efficient for companies to pay for cheap overseas labor.
As far as the "Age of Consumerism" is concerned, consider that at the close of WWII the US was the only modern nation with an intact industrial base, and all that wartime production could be turned into consumer goods.