When the Second Sino-Japanese War broke out between China and Japan in 1937, Peking University, Tsinghua University and Nankai University merged to form Changsha Temporary University in Changsha and later National Southwestern Associated University (Lianda) (traditional Chinese: 國立西南聯合大學; simplified Chinese: 国立西南联合大学; pinyin: Guólì Xīnán Liánhé Dàxué) in Kunming and Mengzi, in Southwest China's Yunnan Province. After the war, the universities moved back and resumed their operation. What was left behind in Kunming became the National Kunming Normal University which later emerged as the Yunnan Normal University.
By summer 1937, the Imperial Japanese Army had bombed Nankai University to the ground in Tianjin and occupied areas including the campuses of two of the country's leading universities in Beijing: Peking University and Tsinghua University. These three universities, which were some of the country's most prestigious, modern institutions of higher learning and research, with the agreement of those who led the institutions — men of high standing who had been educated abroad — retreated to Changsha, the capital city of Hunan province (about 900 miles away from Beijing) to unite. By the middle of December 1937, many students had to leave to fight the Japanese when the city of Nanjing fell to enemy forces.