Some major ways that WWII did this include:
- It set up the Cold War. WWII left the United States and the Soviet Union as the two strongest countries in the world. It did not cause them to be ideological rivals, but it did cause them to be the strongest countries (because the US was untouched by the war and the Soviet Union was harmed much less than Western Europe), which allowed the Cold War to happen.
- It led to the GI Bill. This really changed American society by doing things like letting more people go to college and own their own homes.
- It made the US the leading economic power in the world. The US was untouched by the war (outside, of course, of all the people who died or were wounded). All the other countries that had been major economic powers were devastated. This led to a situation in which the American economy boomed for about 20 years and American standards of living rose rapidly.