What spurred economic growth in the united states during the first half of the 1900s?

The World Wars, since the United States brought in money from other countries, sometimes on credit, by selling food, weapons, and other goods, to waring countries that had a high percentage of their own population focusing on the war. For example, the U.S. sold food to Germany, since they were depleting on food production from their own country. The U.S. also sold/traded weapons to the Allies, and Oil to Japan during WWII. (the stopping of exporting oil and such goods to Japan was the reason why the Japanese attacked pearl harbor, to try and scare/force the U.S. into trade again, but backfired obviously, since the U.S. now entered the war because of the attack)

The theory is land mass basically what they said.