World War I brought the country into a "wartime economy" state, which required large amounts of production for the military sector. Although the U.S. was not completely involved in the war until later on, they did produce a lot of goods for their allies in the United Kingdom, who were on the front lines. Once the U.S. entered the war, the country had to produce a lot more for their troops as well, and led the nation out of the recession it had in the beginning of the 1900's. People also purchased war bonds in patriotic spirit, which also led to and economic rise.
Ultimately, this all led to the economic boom and golden age which we know as the Roaring Twenties.
