In April 1928, Chiang Kai-shek proceeded with the Second Northern Expedition and was approaching Beijing near the end of May. The Beiyang government in Beijing was forced to dissolve as a result; Zhang Zuolin abandoned Beijing to return to Manchuria and was assassinated in the Huanggutun incident by the Japanese Kwantung Army. Immediately after the death of Zhang Zuolin, Zhang Xueliang returned to Shenyang to succeed his father's position. On July 1 he announced an armistice with the National Revolutionary Army and proclaimed that he would not interfere with the reunification. The Japanese were dissatisfied with the move and demanded Zhang to proclaim the independence of Manchuria. He refused the Japanese demand and proceeded with unification matters. On July 3 Chiang Kai-shek arrived in Beijing and met the representative from the Fengtian clique to discuss a peaceful settlement. This negotiation reflected the scramble between the US and Japan on her sphere of influence in China because the US supported Chiang Kai-shek unifying Manchuria. Under pressure from the US and Britain, Japan was diplomatically isolated on this issue. On December 29 Zhang Xueliang announced the replacement of all flags in Manchuria and accepted the jurisdiction of the Nationalist government. Two days later the Nationalist government appointed Zhang as commander of the Northeast Army. China was symbolically reunified at this point.