But there was another facet to the American reform tradition, one that stressed mass action and civil disobedience, and the period between the March on Washington Movement in 1940 and the threat of a black boycott of the draft in 1948 witnessed the beginnings of a shift in the civil rights movement to this kind of reform tactic. The articulate leaders of the prewar struggle were still active, and in fact would make their greatest contribution in the fight that led to the Supreme Court's pronouncement on school segregation in 1954. But their quiet methods were already being challenged by A. Philip Randolph and others who launched a sustained demand for equal treatment and opportunity in the armed forces during the early postwar period. Randolph and leaders of his persuasion relied not so much on legal eloquence in their representations to the federal government as on an understanding of bloc voting in key districts and the implicit threat of civil disobedience. The civil rights campaign, at least in the effort to end segregation in the armed forces, had the appearance of a mass movement a full decade before a weary Rosa Parks boarded a Montgomery bus and set off the all-embracing crusade of Martin Luther King, Jr. The growing political power of the Negro and the threat of mass action in the 1940's were important reasons for the breakthrough on the color front that began in the armed forces in the postwar period. For despite the measure of good will and political acumen that characterized his social programs, Harry S. Truman might never have made the effort to achieve racial equality in the services without the constant pressure of civil rights activists. The reasons for the transformation that was beginning in the civil rights struggle were varied and complex.[5-1] Fundamental was the growing urbanization of the Negro. By 1940 almost half the black population lived in cities. As the labor shortage became more acute during the next five years, movement toward the cities continued, not only in the south but in the north and west. Attracted by economic opportunities in Los Angeles war industries, for example, over 1,000 Negroes moved to that city each month during the war. Detroit, Seattle, and San Francisco, among others, reported similar migrations. The balance finally shifted during the war, and the 1950 census showed that 56 percent of the black population resided in metropolitan (p. 125) areas, 32 percent in cities of the north and west.[5-2]