Tolong jelaskan mengenai Sumber dari Xu Shuzheng

陈贤庆 (Chen Xianqing), 民国军阀派系谈 (The Republic of China Warlord Cliques Discussed), 2007 revised edition

Edward A. McCord, The Power of the Gun: the Emergence of Modern Chinese Warlordism, Berkeley, University of California Press, 1993

Arthur Waldron, From War to Nationalism, Cambridge, Cambridge University Press, 1995