听力原文： Although no longer slaves after the Civil War, American blacks took no significant part in the life of white America except as servants or laborers. Many thousands of them emigrated from the war-destructed South to the North from 1865 to 1915 in the hope of finding work in the big industrial cities. Whole communities of blacks crowded together into ghettos in New York City, Chicago and Detroit, where once the poor white immigrants had lived. These ghettos, neglected by the city authorities, became slums. The schools to which blacks children went were hopelessly inadequate. Unemployment in black ghettos remained consistently higher than in white communities. Stable families were difficult to maintain. Unemployed fathers would on occasion walk out of their homes and never return. Children neglected by their parents turned in some instances to drugs and crimes. The black ghettos are dangerous both for blacks and non-blacks. It is said that television had an enormous influence on frustrated and bitter blacks, for it showed them how much better whites on the whole lived than blacks. There were serous riots in many cities. Radical blacks demanded a free black state within the Union, and advocated violence to achieve that end and to protect themselves against what they felt was police brutality toward blacks. The American blacks emigrate from the South to the North from 1865 to 1915 in order to _________.