evidence: The Yalu River (Chinese: 鸭绿江; pinyin: Yālù Jiāng) or Amnok River (Korean: 압록강; MR: Amnokkang) is a river on the border between China and North Korea. Together with the Tumen River to its east, and a small portion of Paektu Mountain, the Yalu forms the border between China and North Korea. Its valley has been the scene of several military conflicts in the past centuries. It borders North Korea to the south and China to the north. [...] Two other theories exist for the name Yalu: one theory is that the name derived from Yalu ula (ᠶᠠᠯᡠ ᡠᠯᠠ) in the Manchu language. The Manchu word yalu (ᠶᠠᠯᡠ) means "the boundary between two countries". In Mandarin Chinese, yālù phonetically approximates the original Manchu word, but literally means "duck green", which was said to have been once the color of the river. The other theory is that the river was named after the combination of its two upper branches, which were called "鴨" (Yā or Ap) and "綠" (Lù or R(or n)ok)", respectively.[1] [...] According to one scholar, the Korean-Chinese border along the Yalu River is the longest unchanged international border in history, lasting for at least 1,000 years.[13][14][15]