Tang Degang is a historian and biographer who specializes in oral history. In the latter half of his life, he settled in the United States and taught at Columbia University and the City University of New York. In the field of history, he put forward the "Three Gorges Theory of History", which divides the change of Chinese social system into three major stages: feudalism, imperialism, and civil rule. The book was originally titled <i>Mao Zedong's Dictatorship, 1949~1976</i>, but was renamed <i>Thirty Years of New China </i> when it was released on the mainland.