The military history of the Soviet Union began in the days following the 1917 October Revolution that brought the Bolsheviks to power. The new government formed the Red Army to fight various enemies in the Russian Civil War. The years 1918-1921 saw Red Army's defeats in Polish-Soviet war and Estonia, Latvia and Lithuania independence wars. In the late 1930s, the Red Army invaded Finland; fought a brief undeclared border war (together with its ally Mongolia) with Japan and its client state Manchukuo; and, was deployed when the Soviet Union, in agreement with Nazi Germany, took part in the partition of Poland, annexed the Baltic States, Bessarabia and Northern Bukovina (from Romania). In World War II, the Red Army was the major military force in the defeat of Nazi Germany. After the war, it occupied part of Germany and many nations in central and eastern Europe, which became satellite states in the Soviet bloc.
The Soviet Union became the sole superpower rival to the United States. The Cold War between the two nations led to military buildups, the arms race, and the Space Race. By the early 1980s, the Soviet armed forces had more troops and nuclear weapons than any other nation. The Soviet Union fell in 1991, thanks not to military defeat but economic and political factors (see history of the Soviet Union (1985-1991)).
The Soviet military consisted of five armed services. In their official order of importance, the Soviet armed services were the Strategic Rocket Forces, Ground Forces, Air Forces, Air Defense Forces, and Naval Forces. The two other Soviet militarized forces were the Internal Troops (MVD Troops), subordinated to the Ministry of the Interior, and the Border Troops, subordinated to the KGB.