<P> During two waves of massive migration within the United States in the first half of the 20th century, more than 6 million African Americans moved from the South to Northeastern, Midwestern and Western industrial cities, with 5 million migrating from 1940 to 1970 . Some were elected to national political office from their new locations . During the Great Depression, many black voters switched allegiances from the Republican Party to the Democratic Party, in support of the New Deal economic, social network, and work policies of Franklin D. Roosevelt's administration . This trend continued in the 1960s when the national Democratic Party supported the civil rights legislation to enforce constitutional rights . At the same time, there was a different movement among whites in the South, who began to vote for Republican candidates for national and then state offices . </P> <P> A total of 153 African Americans have served in the United States Congress, mostly in the United States House of Representatives . This includes six non-voting members of the House of Representatives who have represented the District of Columbia and the U.S. Virgin Islands . In addition, John Willis Menard was elected to the House of Representatives in 1868, and P.B.S. Pinchback was elected both to the House of Representatives and the Senate in 1872, but neither was seated due to election disputes . </P> <P> Ten African Americans have served in the U.S. Senate, four in the Republican Party . Two African Americans served as Senators from Mississippi during the Reconstruction Era and one from Massachusetts during the 1960s and 1970s . The remaining seven served more recently: six Democrats, three from Illinois (including Barack Obama) and one each from Massachusetts, New Jersey and California; and one Republican from South Carolina . </P> <P> The right of blacks to vote and to serve in the United States Congress was established after the Civil War by amendments to the Constitution . The Thirteenth Amendment (ratified December 6, 1865), abolished slavery . The Fourteenth Amendment (ratified July 9, 1868) made all people born or naturalized in the United States citizens . The Fifteenth Amendment (ratified February 3, 1870) forbade the denial or abridgment of the right to vote on account of race, color, or previous condition of servitude, and gave Congress the power to enforce the law by appropriate legislation . </P>

How many african american politicians served in the us congress during reconstruction