Relations between the Soviet Union and Japan between the Communist takeover in 1917 and the collapse of Communism in 1991 tended to be hostile. Japan had sent troops to counter the Bolshevik presence in Russia's Far East during the Russian Civil War, and both countries had been in opposite camps during World War II and the Cold War. In addition, territorial conflicts over the Kuril Islands and South Sakhalin were a constant source of tension. These, with a number of smaller conflicts, prevented both countries from signing a peace treaty after World War II, and even today matters remain unresolved.