When the Japanese invaded Shanxi, the Red Army (renamed the Eighth Route Army) assisted the Kuomintang warlord, Yan Xishan, in resisting the Japanese, and Peng traveled to the provincial capital, Taiyuan, with Zhou Enlai to co-ordinate tactics. After the Japanese advanced towards Taiyuan on September 13, 1937, Peng directed overall operations from a base in Wutaishan but was called from duty to attend a Politburo meeting on December 13. At the meeting, Peng advocated a greater material commitment to the defense of Shanxi, but Mao disagreed and wanted the Red Army to reduce its commitment to fighting the Japanese. In 1938, after Mao's rival, Zhang Guotao, defected to the Kuomintang, Peng moved closer to Mao's position. In late 1938, Peng set up a base in Taihangshan, on the borders of Shanxi and Hebei, and directed guerrilla operations in both provinces. From Taihangshan, Peng commanded two thirds of the Eighth Route Army, approximately 100,000 soldiers.