The Battle of Lake Khasan, also known as the Changkufeng Incident, was an attempted military incursion by Manchukuo, a Japanese puppet state, into territory claimed and controlled by the Soviet Union. The incursion, which occurred from 29 July to 11 August 1938, 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 had subsequently tampered with the demarcation markers. Japanese forces occupied the disputed area but withdrew after heavy fighting and a diplomatic settlement.