Through a Confucian lens, this research explores the transformation of the Kuomintang’s (國民黨; KMT) foreign policy during the 1920s. It examines the shift in the KMT's foreign policy from Sun Yat-Sen’s 孫逸仙 (1866-1925) “Allying with Soviet Russia” (lian’e 聯俄) stance to Chiang Kai-shek’s 蔣介石 (1887-1975) prioritization of Western relations around 1927. The study highlights the reintroduction of Confucianism in the KMT's foreign policy during this period, considering the conventional Confucian education of KMT leaders. Unlike previous studies analyzing this shift from political or historical perspectives, this study provides a chronological analysis that centers around the change to Confucianism. It addresses a significant research vacuum in the existing literature and uses archival analysis to examine the evolution of the KMT’s foreign policy. The study examines primary sources such as Sun’s speeches, Chiang's diary, and contemporaneous memoirs. The study comprises three chronological sections. The first section (1920–1924) explores the influence of Confucianism on Sun’s alignment with Soviet Russia due to commonalities between Confucianism and Communism. The second section (1924-1927) examines how Confucianism shaped the KMT’s Western-oriented shift. The third section (1928–1930) delves into the philosophical basis of the Treaty Revision Movement (Gaiding xinyue yundong 改訂新約運動) and the adoption of ‘keeping good faith and pursuing harmony’ (Jiangxin xiumu 講信修睦) as the foreign policy principle. This research concludes that Sun, inspired by Confucian-Communist parallels, initially aligned with Soviet Russia but that later, under Chiang’s leadership, the KMT used “The Confucianisation of the Three People’s Principles” (Sanminzhuyi 三民主義) in its consolidation of a power shift towards the West and adopted Confucian principles to further legitimize its rule by promoting the New Treaty Movement.