We typically think that the Civil Rights Movement started with Rosa Parks in late 1955. While this is true in many ways, we should not ignore the fact that there were important changes between the end of World War II and 1955.
There are only two milestones from this period that most Americans know about. These are the debut of Jackie Robinson as the first African American in Major League Baseball in 1947 and the 1954 Supreme Court decision in Brown v. Board of Education, which made segregation in public schools illegal. However, there were other changes that helped to improve conditions for African Americans during this time.
Baseball was not the only thing that desegregated during these years. In 1949, the army adopted a new policy that allowed African Americans to serve in any position for which they were qualified. The navy and the air force did the same. This led to the integration of military units during the Korean War. In addition, in 1948 President Harry Truman issued an executive order that banned discrimination in federal employment. In terms of housing, that year also saw the Supreme Court issue a ruling in Shelley v. Kraemer that prevented governments from enforcing private contracts (called “restrictive covenants”) that prohibited whites from selling their homes to blacks. This made it more possible for neighborhoods to become integrated. In 1950, the Supreme Court decided Henderson v. United States, ruling that segregation in railroad dining cars was illegal.
All this is not to say that things improved tremendously for African Americans during these years. There was still a great deal of discrimination and segregation. However, there were advances made during these years that did improve conditions for African Americans.
Between the years of 1945-1955, African American conditions did improve, but ever so slightly. Following their contributions to the Second World War, people began thinking about how African Americans deserved better treatment, but it wasn't until after this period where the campaign for more rights really began going into full swing. To put it in simple terms, I would say their conditions during this period improved by means of desegregation, and we can see this in three different ways.
1948-Due to their efforts in WWII, President Truman decides to desegregate the military by means of an executive order.
1954-In Brown vs. Board of Education, the Supreme Court declares that schools must be desegregated. This overturned Plessy v. Ferguson, which stated "separate but equal" and allowed separate schools for blacks and whites.
1955-Due to Rosa Parks refusing to give up her seat in the front of the bus to a white person, the Montgomery Bus Boycott begins. This leads to buses in the Montgomery system being desegregated. Eventually, the Federal Interstate Commerce Commission prohibits segregation on interstate trains and buses.
The Montgomery Bus Boycott also introduced Martin Luther King Jr. as a prominent civil rights leader, and ushered in the movement that would dominate the 1960s.