北伐是中華民國建立以來再度結束政府分裂狀態邁向統一的關鍵，也是蔣介石畢生軍政之功的第一座里程碑。從現代中日關係的歷史脈絡來說，北伐卻是蔣介石與日本關係從友變敵的分界線。蔣介石早年留學日本，對日本的現代化有成，素有仰慕之心。再則，他師承孫中山所倡導的「大亞洲主義」，衷心期盼中日兩國能相互提攜共謀亞洲大局。是以，北伐之初，蔣介石與日本政府保持密切聯繫，始終渴望得到日本相助之力。可是，日本政府對北伐所持的基本態度，卻以北伐軍是否會進入華北領域為依歸。北伐初期，因興起於華南地區，非日本勢力範圍區，日本政府並未特別重視。日本政府開始注意北伐，是北伐勢力從華南地區進入華中地區以後。如何挑動北伐軍內部反共勢力與親共勢力的矛盾，誘導反共勢力與親共勢力劃清界限，則為日本政府面對北伐新情勢的對應方略。因此，蔣介石在上海實施全面清黨，日本政府則全力配合，對於南京政府的成立更是傾力支援。可是，一旦北伐軍進入華北領域以後，日本政府不僅反對，甚至還不惜以護僑為藉口，三度出兵山東省，企圖以武力公然阻礙北伐。

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.