In "The Central Theme of Southern History" (1928), Phillips maintained that the desire to keep their region "a white man's country" united the white southerners for centuries. Phillips' emphasis on race was overshadowed in the late 1920s and 1930s by the Beardian interpretation of Charles A. Beard and Mary Ritter Beard, who in their enormously successful "The Rise of American Civilization" (1927) emphasized class conflict and downplayed slavery and race relations as a cause of the American Civil War. By the 1950s, however, the Beardian economic determinism was out of fashion, and the emphasis on race (rather than region or class) became a major topic in historiography.