That change in policy came while Japan was in the midst of a severe economic crisis from the 1923 Great Kantō earthquake and successive economic depressions, and it caused both alarm and irritation in the Kwantung Army leadership. The situation was further complicated by the success of the Northern Expedition, led by Chiang Kai-shek of the National Revolutionary Army, in which the Kuomintang successively defeated Sun Chuanfang, Wu Peifu and other warlords of the Northern Faction and the Beijing government, controlled by Zhang Zuolin. The Nationalists appeared poised to restore their rule over Manchuria, which was still officially claimed as part of the Republic of China.