Complex sentence: In 1945, with the defeat of Japan in World War II, the Japanese administration in Karafuto ceased to function, and in 1951, at the Treaty of San Francisco, Japan renounced its rights to Sakhalin.
Split into simpler sentences: In 1945, with the defeat of Japan in World War II, the Japanese administration in Karafuto ceased to function. In 1951, at the Treaty of San Francisco, Japan renounced its rights to Sakhalin.