The Battle of Lake Khasan (29 July – 11 August 1938), also known as the Changkufeng Incident (Russian: Хасанские бои, Chinese and Japanese: 張鼓峰事件; Chinese pinyin: Zhānggǔfēng Shìjià; Japanese romaji: Chōkohō Jiken) in China and Japan, was an attempted military incursion by Manchukuo, a Japanese puppet state, into the territory claimed and controlled by the Soviet Union. That incursion was founded in the Japanese belief that the Soviet Union had misinterpreted the demarcation of the boundary based on the Treaty of Peking between Imperial Russia and Qing China and the subsequent supplementary agreements on demarcation and tampered with the demarcation markers. Japanese forces occupied the disputed area but withdrew after heavy fighting and a diplomatic settlement.