Operation August Storm, or the Battle of Manchuria began on August 8, 1945, with the Soviet invasion of the Japanese puppet state of Manchukuo; the greater invasion would eventually include neighboring Mengjiang, as well as northern Korea, southern Sakhalin, and the Kuril Islands. It marked the initial and only military action of the Soviet Union against the Empire of Japan; at the Yalta Conference, it had agreed to Allied pleas to terminate the neutrality pact with Japan and enter the Second World War's Pacific Theater within three months after the end of the war in Europe.