World War I led to an economic and industrial boom, as factory owners known as "Merchants of Death" made billions off of supplying the Allies war effort. It created a vibrant middle class in this country that would strengthen all the way through the 1920s.
World War II, on the other hand, benefited us first by taking us out of the Great Depression once and for all. The massive numbers of jobs it created, both in and out of the military, jumpstarted our economy. Again, we supplied the allies with war material as well as outfitted our own massive armies.
The aircraft giant Boeing was put on the map making bombers for World War II, and scores of other companies and factories were created with military contracts that turned commercial when the war was over, and brought us millions of jobs for the rest of the century.