After the Kuomintang (KMT), the governing party of China, unified the country in the 1920s, the civil war between it and its past ally Communist Party of China began. In 1931, Japan used the Mukden Incident as a reason to take Manchuria and set up its puppet state, Manchukuo, while the League of Nations could not do anything to stop it. The Tanggu Truce, a ceasefire, was signed in 1933. In 1936, the KMT and the communists agreed to stop fighting against each other to fight Japan instead. In 1937, Japan started a Second Sino-Japanese War to take the rest of China.