John G. Gurley’s Challengers to Capitalism: Marx, Lenin, Stalin, and Mao (W. W. Norton, 1980; later editions by Addison-Wesley, 1988) is a critical study of the major figures who opposed capitalist systems. Gurley, an economist at Stanford University, examines the theories and practices of Marx, Lenin, Stalin, and Mao, analyzing their ideological contributions and the historical impact of their leadership. The book is part of The Portable Stanford series and runs about 225–239 pages depending on edition.