Though a close associate of Duan Qirui, Shanxi's military governor, Yan Xishan, did not join Duan's Anhui clique. He kept his province neutral from the various civil wars the nation was facing. He would fight troops from other cliques if they encroached the provincial boundaries. In 1927, faced with the overwhelming forces of the National Revolutionary Army, the Fengtian clique issued an ultimatum to Yan to join their side. Yan joined the NRA instead and drove Fengtian armies from Beijing. As a reward, the Kuomintang allowed the Shanxi clique to expand all the way to the sea at Hebei, Shandong. Displeased with the dictatorship of Chiang Kaishek, the Shanxi clique together with several other cliques launched the Central Plains War but was defeated. The clique was significantly weakened by the Japanese invasion which occupied most of their base province. After the war, Yan was unable to defend his province which fell to the Communists in 1949.