After World War II, African Americans continued facing widespread legal and social segregation despite some gains. They began challenging segregation through legal and protest efforts, including the historic 1954 Brown v. Board of Education Supreme Court ruling declaring segregated schools unconstitutional, and the 1955 Montgomery bus boycott organized by Martin Luther King Jr in response to Rosa Parks' arrest. However, massive resistance to desegregation persisted through the late 1950s, such as when the National Guard blocked African American students from attending a desegregated high school in Little Rock, Arkansas in 1957.