Sino-Soviet border conflict
In the 1960s, Manchuria's border with the Soviet Union became the site of the most serious tension between the Soviet Union and China. The treaties of 1858 and 1860, which ceded territory north of the Amur, were ambiguous as to which course of the river was the boundary. This ambiguity led to dispute over the political status of several islands. This led to armed conflict in 1969, called the Sino-Soviet border conflict.