Previous studies of China's civil war have concentrated on different aspects and causes leading to the Communist victory and focused on political, economic, and military explanations. Few studies, however, have examined the features of foreign intervention and assistance to the Communist Party of China and their contribution to the latter's success. Sino-Soviet relations and cooperation during the war have received the attention of several studies, but the role of North Korea in the war has remained obscure. As information regarding North Korea's actions during China's civil war remains largely inaccessible, few studies have debated the question of whether North Korea had ever deployed its forces in China's Northeast in order to assist their Chinese comrades. Relying on military and intelligence documents from the Republic of China, this article shows how by the time of the Soviet withdrawal from China's Northeast, the USSR had become resolute about turning North Korea into a militarized state in order to protect its own interests in the region and assist the Chinese Communists.