By participating in World War II the American society switched to a whole new axis in terms of policies and society. Pre-World War II Americans were very rigid and isolationists with many policies and rules, even in universities following religious leadership and pro-community. During the war and directly afterward, the local community began to suffer from a lack of workers and low economic movement which drove many families towards bigger cities (exactly as the Great Depression did a decade before). Post-war our policies turned to intervention and inclusion, in some regards. Before we stayed away from the politics of the world, hence our decision to not join the League of Nations twenty years before. Now after this war we decided it was time to be a recognizing force, which directly put us against the USSR, and the Cold War was born (there are many other factors that have not been mentioned). Yet in the 1930s President Franklin D. Roosevelt was wanting to move American society away from being isolated anyways but there were policies that halted his advances (military humor).
So to conclude, participating in World War II completely changed American society and helped us finally reach out a hand and help those who would otherwise have trouble. We showed that we can be a trusted ally and a formidable foe, but we also showed that our society was not rooted in isolation, but was very adaptable and ready for a change. A change which we still feel today as our policies are ever moving outward and surrounding this globe.