During and after World War II,challenges to segregation (種族隔離) became more common and more successful.Three major factors accounted for this The Great Migration The great migration was the movement of blacks from the Southern states to the Northern and Western ones for a range of reasons including better jobs,better schools,and a less racist environment.It began during World War I,continued during the 1930s,and expanded dramatically in the 1940s and 1950s.The great migration introduced millions of blacks to a world in which formal segregation did not exist and basic facilities,like transportation,restaurants,and public bathrooms,were open to all people.However,the North was not without racism.Blacks could not move to certain neighborhoods,were denied access to many jobs,and were informally segregated.But,despite segregation and exclusion by individuals,unions,and employers,blacks who moved to the North were able to live without the oppression of day-to-day segregation.They were thus better able to oppose legalized segregation in the South.Changes in American Politics While the great migration changed how black Americans lived,the Great Depression of the 1930s and the New Deal altered American politics by setting a precedent for government activism.The administration of President Franklin Roosevelt assumed a new role of intervening in society to ensure jobs,justice,and the prosperity of the American people,who were severely affected by the Depression.Roosevelt himself was progressive on race and appointed blacks to high offices.The president’s wife,Eleanor Roosevelt,made clear her hatred for segregation.In a gesture that symbolized a sharp break with previous administrations,she invited the National Council of Negro Women to have tea at the White House.By the eve of World War II,black voters regularly elected officials in a number of Northern states.These newly elected officials actively fought against segregation and racism although not always successfully.Social and Cultural Changes A final drive to the civil rights movement was World War II.The struggle against Nazism forced some Americans to reconsider the legitimacy (合法性) of racism in the United States.The Holocaust (大屠殺) of six million Jews,merely because of their ethnicity (種族),led some Americans to realize that racism could be a threat to democracy itself.Blacks also served in the military in unprecedented numbers.Thus,the war experience taught many people that equality was possible.Following the war,black veterans returned with a new sense of purpose.Joining them in the struggle against segregation was a better-educated and financially more secure black middle class living in the North.Many blacks had earned high wages in war industries,were members of industrial unions,and politically active.Finally,the postwar world forced the government to face the threat that segregation posed to international relations.After the war,many colonies in Asia and Africa gained their independence from European domination.At the same time,the Cold War struggle with the Communist government of USSR (前蘇聯(lián)) forced the United States to seek the good will of these nations.Segregation undermined the nation’s ability to negotiate with these new nations while giving the USSR ammunition in its propaganda war against the United States.Leaders of the American foreign policy establishment urged an end to segregation at home as a way of fighting Communism abroad.