The Northern Expedition was not merely the key bringing an end to the warlord period and reunifying China, it was also a milestone for Chiang Kai-shek to bring order out of chaos. But from the perspective of modern Sino-Japanese relations, the Northern Expedition also marked the beginning of a process that turned the relations between Chiang Kai-shek and Japan from friendship to enmity. Chiang Kai-shek studied in Japan in his early years and admired its modernization. Moreover, as a disciple of ”the greater-Asia doctrine” that Sun Yat-sen had advocated, Chiang expected China and Japan sincerely and mutually to guide and support the overall situation of Asia. Therefore, from the beginning of the Northern Expedition, it is clear that Chiang repeated contacted Japanese government and eagerly sought its aid. However, the consistent attitude of the Japanese government to the Northern Expedition basically rested on the concern that Chiang's army would not enter northern China. Initially, the Japanese government did not pay attention to North Expedition's actions because the Northern Expedition Army begun the battle from Southern China, a region that was not a concern of the Japanese government. It wasn't until when the Northern Expedition Army entered Central China, that the subversion of Kuomintang-the Communist alliance became the important Japan's Policy towards the Northern Expedition. This is why when Chiang Kai-shek carried out a sweeping purge of Communists in Shanghai; the Japanese government applauded his action and was inclined to support him. But, once the Northern Expeditionary Army entered the field of North China, the Japanese government was not merely in opposition, but also, on the pretext of protecting Japanese abroad, again dispatched troops to Shandong to open hinder the Northern Expedition by force.