As agreed at Yalta , the Soviet Union had intervened in the war with Japan within three months of the German surrender , and they were therefore entitled to annex the territories of South Sakhalin and the Kuril Islands and also to preeminent interests over Port Arthur and Dalian , with its strategic rail connections , via the China Changchun Railway , a company owned jointly by China and the Soviet Union that operated all the railways of the former Manchukuo . The territories on the Asian mainland were transferred to the full control of the People 's Republic of China in 1955 ; the other possessions are still administered by the Soviet Union 's successor state , Russia
Yalta
Yalta Conference
Soviet–Japanese War