within a short span of time. World War II The Soviet Union entered World War II on 17 September 1939 with its invasion of Poland, in accordance with a secret protocol within the Molotov–Ribbentrop Pact with Nazi Germany. The Soviet Union later invaded Finland, and occupied and annexed the Baltic states, as well as parts of Romania. On 22 June 1941, Germany invaded the Soviet Union, opening the Eastern Front, the largest theater of World War II. Eventually, some 5 million Red Army troops were captured by the Nazis; the latter deliberately starved to death or otherwise killed 3.3 million Soviet POWs, and a vast number of civilians, as the "Hunger Plan" sought to fulfill Generalplan Ost. Although the Wehrmacht had considerable early success, their attack was halted in the Battle of Moscow. Subsequently, the Germans were dealt major defeats first at the Battle of Stalingrad in the winter of 1942–1943, and then in the Battle of Kursk in the summer of 1943. Another German failure was the Siege of Leningrad, in which the city was fully blockaded on land between 1941 and 1944 by German and Finnish forces, and suffered starvation and more than a million deaths, but never surrendered. Soviet forces steamrolled through Eastern and Central Europe in 1944–1945 and captured Berlin in May 1945. In August 1945, the Red Army invaded Manchuria and ousted the Japanese from Northeast Asia, contributing to the Allied victory over Japan. The 1941–1945 period of World War II is known in Russia as the Great Patriotic War. The Soviet Union, along with the United States, the United Kingdom and China were considered the Big Four of Allied powers in World War II, and later became the Four Policemen, which was the foundation of the United Nations Security Council. During the war, Soviet civilian and military death were about 26–27 million, accounting for about half of all World War II casualties. The Soviet economy and infrastructure suffered massive devastation, which caused the Soviet famine of 1946–1947. However, at the expense of a large sacrifice, the Soviet Union emerged as a global superpower. Cold War After World War II, parts of Eastern and Central Europe, including East Germany and eastern parts of Austria were occupied by Red Army according to the Potsdam Conference. Dependent communist governments were installed in the Eastern Bloc satellite states. After becoming the world's second nuclear power, the Soviet Union