From the Treaty of Nerchinskin 1689 to the Treaties of Aigun in 1857 and Peking in 1860, this vast territory comprised Manchuria north of the Amur and east of the Ussuri rivers. It is bounded by the Stanovoi mountains to the north and the Gulf of Tartary to the east, the Amur-Ussuri forming the southern and western limits. It was ceded by the Manchu Empire to Russia in two stages and from 1860 to 1920 was, as Russian Manchuria, part of the Russian Empire. From 1920 to 1925 Outer Manchuria was occupied by the Japanese and briefly united with Inner Manchuria under Japanese domination. From 1925 on, as Soviet Manchuria, it formed part of the far eastern provinces of the USSR and was used as the launch-pad for the Soviet assault on Japanese occupied Inner Manchuria in 1945, when Manchuria was again briefly united under Soviet rule. In 1949, Inner Manchuria was returned to communist China. In 1959 tension arose between Chinese Inner Manchuria and Russian Outer Manchuria over the interpretation of the treaties of Aigun and Peking. This was as much an attempt to undo European colonialism as an ideological split between Mao Tse-tung and Khrushchov.