WWII changed the distribution of power in the world. Germany and Japan were defeated, Europe was in shambles and most of the European countries were losing their colonies (example: India and Pakistan gained independence from the UK in 1947, etc.). The US and USSR emerged as the main superpowers and polarized the world around them.
The US achieved the most dramatic changes as compared to any other country. Not only did it emerge victorious, it also cemented its position as a rich and powerful nation. This new-found confidence in its abilities helped the US achieve a great number of things.
The most important of these changes was the introduction of the GI bill that offered the returning soldiers an easier assimilation into society by offering college tuition, cheap loans for homes and business, etc. Women were also part of the war industry and began gaining equal rights. The formerly oppressed communities, such as African- Americans and Latin Americans, began exerting their demands for equal status. Domestically, the US spent a great deal of capital on infrastructure development, enriching its human resources, increasing industrial output and also building up its arsenal for exerting its authority over the rest of the world.
Another big change in domestic policies was related to the emergence of suburbs, areas close to cities but cheaper than cities for living. This was made possible by better infrastructure and facilities.