In June 1926, Zhang managed to capture Beijing, and rumours swirled that he was planning to proclaim himself emperor. Instead, a year later, with Kuomintang forces rapidly closing in, he combined his military forces with those of the other warlords, including Zhang Zongchang and Sun Chuanfang, into the National Pacification Army and fought against the Northern Expedition. At the same time, he proclaimed himself Generalissimo of the Republic of China, and thus led China's internationally recognized government as a dictator. However, the Nationalists led by Chiang Kai-shek attacked his forces and in May 1928 the Fengtian Army had to retreat towards Beijing. In addition, Japan applied pressure on Zhang to leave Beijing and return to Manchuria, and underscored this by bringing reinforcements to Tianjin. Zhang left Beijing on 3 June 1928.