As the previous educator mentioned, the role of the United States in the Second World War cemented its status, not only as a global leader, but also as a nation responsible for leading democracy and the expansion of democratic values throughout the world. For some, this new role brought cause for concern.
In his farewell address to the nation, President Eisenhower warned against the development of the "military-industrial complex." He was concerned by the nation's development of a permanent arms industry outside of wartime, and worried that the U.S. might acquire undue influence through its massive military power. Eisenhower believed in the importance of defense, but also wanted the nation to play a strong diplomatic role.
Though Truman was the nation's first post-war president who led his own reforms, including the integration of the military, the years after World War II are often referred to as the Eisenhower Era. In regard to infrastructure, the nation's federal highway system was built in the 1950s. This not only simplified interstate commerce, it also allowed people to travel across the nation by car and allowed for the possibility of whites to move to the suburbs. This left many inner-cities filled predominately with minorities who, due to their poverty and diminished property values, often lived in crumbling neighborhoods.
Eisenhower was also responsible for the appointment of Chief Justice Earl Warren to the Supreme Court. It was the Warren Court that decided in Brown v. Board of Education of Topeka, Kansas that school segregation was unconstitutional under the "equal protection" clause of the Fourteenth Amendment. This decision allowed for further challenges to Jim Crow laws in the South and the de facto discrimination in Northern cities. However, legal discrimination did not end until 1964 with the passage of the Civil Rights Act, and legal voting discrimination did not end until 1965 with the passage of the Voting Rights Act.
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.