Well, it was a slow process of decline. The peak of greatness was somewhere from 1945 to 1960. Everybody bought American cars, "Made in America" meant quality and a lot of things were made here, we won wars and they were usually declared by Congress (Korea being an early exception), Hollywood made films that were great and not filled with cursing and graphic sex and violence, people respected the flag and authority, drugs were so taboo that people didn't dare mention them in casual conversation. America was respected all over the world.
Cultural change=The DESTRUCTION OF AMERICA!!1!1
The legacy of the new deal was very strong in the 40s and 50s.
Lol.
That is slightly more articulate.