approximately 2.8 million in 1948. In order to control this demobilisation process, the number of military districts was temporarily increased to thirty-three, dropping to twenty-one in 1946. The size of the Ground Forces throughout most time of the Cold War remained between 4 million and 5 million, according to Western estimates. Soviet law required all able-bodied males of age to serve a minimum of 2 years. As a result, the Soviet Army remained the largest active army in the world from 1945 to 1991. Soviet Army units which had taken over the countries of Eastern Europe from German rule remained in some of them to secure the régimes in what became satellite states of the Soviet Union and to deter and to fend off pro-independence resistance and later NATO forces. The greatest Soviet military presence was in East Germany, in the Group of Soviet Forces in Germany, but there were also smaller forces elsewhere, including the Northern Group of Forces in Poland, the Central Group of Forces in Czechoslovakia, and the Southern Group of Forces in Hungary. In the Soviet Union itself, forces were divided by the 1950s among fifteen military districts, including the Moscow, Leningrad, and Baltic Military Districts. The trauma of the devastating German invasion of 1941 influenced the Soviet Cold War military doctrine of fighting enemies on their own territory, or in a buffer zone under Soviet hegemony, but in any case preventing any war from reaching Soviet soil. In order to secure Soviet interests in Eastern Europe, the Soviet Army moved in to quell anti-Soviet uprisings in the German Democratic Republic (1953), Hungary (1956) and Czechoslovakia (1968). As a result of the Sino-Soviet border conflict, a sixteenth military district was created in 1969, the Central Asian Military District, with headquarters at Alma-Ata. To improve capabilities for war at a theatre level, in the late 1970s and early 1980s four high commands were established, grouping the military districts, groups of forces, and fleets. The Far Eastern High Command was established first, followed by the Western and South-Western High Commands towards Europe, and the Southern High Command at Baku, oriented toward the Middle East. Confrontation with the US and NATO during the Cold War mainly took the form of threatened mutual deterrence with nuclear weapons. The Soviet Union invested heavily in the Army's nuclear capacity, especially in the production of ballistic missiles and of nuclear submarines to deliver