Why did Sun Yat-sen seek help from the Soviet Union in the 1920s?

In the 1920s, Sun Yat-sen sought assistance from the Soviet Union primarily to secure the necessary support to reunify China and strengthen his Kuomintang (Nationalist) Party. Following unsuccessful attempts to establish a stable government in the south, Sun required external resources to build a viable military and political movement capable of challenging the northern government and overcoming the influence of foreign imperialism.12

Through the Sun-Joffe Manifesto, Sun formalized a partnership that provided the Kuomintang with critical military and political aid. In exchange, Sun agreed to a "United Front," allowing members of the Chinese Communist Party to join the Kuomintang as individuals. This collaboration brought in Soviet advisers, such as Mikhail M. Borodin, who helped reorganize the Nationalist Party and train its military forces, including sending figures like Chiang Kai-shek to Moscow for training in Soviet organizational methods.13