On the whole, the Soviet Union’s primary goal after 1945 was to rebuild whatever lay in ruins within its own borders.
The German invasion had ravaged the infrastructure and population of the USSR, and first and foremost these are what required immediate their attention. As long as the Soviets had food and fuel, they could rebuild their industrial and military-industrial complexes and attempt to escape the burdensome ‘war economy’. Marxism could not hope to last as a viable system if it could not provide bread and avoiding that was arguably the fulcrum of the rebuilding effort.
The occupied territories in E. Europe were under military suppression-at the very least, the neutralisation of potentially hostile forces allowed the USSR proper some breathing space to rebuild. In order to maintain this new ‘buffer zone’, the Soviets needed to feed the millions of troops in Red service but also feed the millions of East Germans, Poles, Hungarians and others so as to avoid the total collapse of that frontier.
More food required more railways and trains to assist in its transportation, but they were also needed to transport troops, fuel and raw materials to the major centres of E. Europe. Poland needed a functioning Warsaw, and Hungary needed a similar Prague; Moscow’s survival was paramount, but that survival required the survival of other cities too.
To fuel the rebuilding of these major centres also meant that the decimated Soviet energy system (largely based around the Caucasus) needed to be expanded to meet the demand. Oil and gas from the Caucasus whilst not directly being harmed by the German invasion had been overworked and needed desperate investment, whilst the major coal bearing regions such as the Donbass area of Ukraine had been obliterated and again demanded attention.
The Soviets were not, contrary to many contemporary beliefs, looking to invade and conquer Western Europe. Stalin was more than happy with his massive gains in the East, and as I have already mentioned his main concern was feeding his people and those under his occupation. In many ways the maintenance of such a huge number of troops was due to their own fears of a Western invasion of E. Europe (as espoused by W. Churchill, e.g. Operation ‘Unthinkable’).
As long as the Soviets could feed its own people and the troops of its enormous military, it could at least focus upon rebuilding its devastated centres. With its own citizens reasonably fed, it could attempt to feed those of Eastern Europe-which in itself required the expansion of railways and the modernisation of its tiring energy system. After 1945, the main goal of the USSR was the aforementioned and the outright survival of Marxism.