I think there is a bit of confusion here that is understandable given the rather wonky USSR had with Great Russian nationality. Ethnic Great Russians may have made up a sizable proportion of the USSR's population and leadership, but the ideology of the USSR was explicitly against placing one nationality over another. Marxist-Leninist thought held that national identification was only a temporary byproduct of capitalist development and would be subsumed by an eventual "New Soviet Man"/Homo Sovieticus that would replace this form of identification.

Homo Sovieticus evolved out of a somewhat complex series of events both before and after 1917. The national question caught Lenin and company somewhat flat-footed in 1917. As Marxists inside an active revolution, they were naturally disinclined to give much weight to the national issue. In classical Marxism, nationalism was a tool of the bourgeoisie and monopoly capital to distract and divide the proletariat from achieving true class consciousness. Although the turn of the century saw the emergence of significant models of how nationalism would fit in a worker's revolution (eg Austromarxism, Cultural-National Autonomy, Personal National Autonomy, etc.), the Bolsheviks found after their seizure of power that they now had to deal with the nationalities question with concrete policies. The Russian empire, whose various state organs were disintegrating as the Bolsheviks stormed the Winter Palace, was majority non-Russian, but a good portion of the Bolshevik leadership and rank and file were Russian or Russified. But this was not the case for the Empire as a whole. Great Russians consisted of approximately 44% of the empire according to the 1897 census, which was the last accurate data set of the empire's population prior to the First World War and even though the census is something of a blunt analytical instrument, it does show there was no dominant ethnic group. The result of this heterogeneity was that Bolshevik leadership tended to move on the nationalities question with a mixture of tactical declarations with the aim of using nationalism to secure the revolution.

This was not entirely successful at first. Lenin boldly declared after the November Revolution that the Bolsheviks championed the right of national self-determination with the aim of encouraging wider revolution. When Finland declared its independence in December 1917, the Bolshevik leadership accepted it in the hopes of that a Finnish communist party would take power, but an anti-communist government took power in Helsinki after a brutal civil war. Likewise experience in the Baltics, where anti-communist nationalists tended to take power with German assistance, meant that Lenin needed to condition his call for national self-determination. This meant Bolshevik responses towards the national issue were often tactical compromises with a clear agenda that nationalism could not work against the wider interests of the revolution.

The historian of tsarist nationalities policies Eric Lohr has described the eighteenth-century tsarist approach to immigration as "attract and hold" meaning that they induced foreign colonists like the Volga Germans to settle and then kept them inside the empire through a variety of state levers. "Attract and hold" is also an apt metaphor for to post-Finnish Bolshevik nationalities policies. The Bolsheviks encouraged the revolution in the vast non-Russian empire and appeals towards nationalism was one of the tools in the Bolshevik's arsenal. The Bolsheviks simply could not ignore nationalism in light of the Civil War lest it be instrumentalized by the Whites. Leaving national movements alone risked another Finland. In Central Asia and the Caucuses, Lenin crafted an appeal to nationalist sentiment by dividing nationalism between exploiter and exploited nations. Bolshevik agitprop materials often emphasized the Great Russian chauvinism of the empire had encouraged a healthy counter-response among the exploited non-Russian masses. However, the Bolshevik approach always called for some sort of mediation of nationalism by the emerging Communist Party. This bifurcated approach towards nationalism, attracting non-Russians with promises of national justice but holding them within an ideological structure, became one of the hallmarks of Soviet nationalities policies. The 1920s saw the introduction of korenizatsiia (indiginzation or as Terry Martin terms it "Soviet affirmative action) in which the Communist Party sought to raise up native cadres of Communist activists inside their own territory. Although the state walked away from korenizatsiia in the 1930s, it never really went away in the USSR and would remain part of the Soviet policy until the end of the USSR in 1991. This imparted a certain political stability to areas like Central Asia in which local elites assumed positions of power within the Communist Party apparatus.

By 1944/45, it was a much more different situation. Although to be clear, the Soviets did annex significant territory from Finland, Poland, Romania, East Prussia, Czechoslovakia, and the Baltics, so sizable portions of Eastern Europe did end up inside the USSR. But Stalin's basic agenda for Eastern Europe was to expand the Soviet sphere of influence and secure the Soviet state (and these two precepts were pretty much indistinguishable in practice). For areas under direct Soviet influence, this meant encouraging local Communist parties to take power, through legal and extra-legal means. Moscow could count on a wide number of emigre Communists to take these posts and nationalism was one of the tools used by these satellite Communist parties to cement their rule. While Communist-style nationalism had yet to achieve the prominence as a legitimization stratagem it would in the 1950s, wartime and postwar propaganda produced by these Eastern European Communist parties stressed a popular front and a desire for the nation to rise up and cast out the foreign German invader and their collaborators.

Preserving national borders, albeit altered for Soviet purposes, also fit into the larger geostrategic designs of Stalin. Not only would massive annexations further rupture the wartime alliance with the Western Allies, it would also be counterproductive for the wider postwar Communist movement. Stalin expected, with some justification, that Western European Communist movements would achieve broad electoral gains in the immediate postwar period. Broad annexations in Eastern Europe would hurt this chance as nationalism still exerted a powerful force and French and Italian Communists were still French and Italian. The time was not yet ripe for the erasure of the nation and its replacement with a Soviet identity. Much the same logic underlay Soviet moves to what Alfred Sauvy coined in 1953 the Third World. The Soviets did recognize that nationalists in the decolonized regions could become allied with Soviet Marxist-Leninism. Marxism was an explicitly anti-imperial "ism" and the USSR did position itself as the global leader for the oppressed nations of the world. Naturally, such an alliance would lead to trading relationships in which the industrialized USSR could provide finished goods in exchange for agricultural products like cotton or coffee that were in short supply in the USSR.

Things, of course, did not play out in the postwar period as Moscow expected. Nationalism became one of the Achilles' heels in Eastern Europe and there was a widespread sentiment that the ruling elite did not really have the nation or the people's best interests at heart. The Soviet's use of hard and soft power to rig Eastern European elections for Communist victory likewise denuded the Communism of much of its postwar prestige in Western Europe. Ironically, the slightly higher standard of living within Eastern Europe and compared to the USSR created a degree of resentment within the wider USSR in the 1970s that their satellites were living better than the leading partner in the Communist experiment. And Third World nationalist leaders like Egypt's Nasser proved incredibly hard to tame as they were leery of the USSR's offers of support because they recognized that the Soviet trading relationship had shades of colonialism despite the USSR's protests to the contrary. The USSR also faced significant rivals in the form of both Mao and Castro, and to a lesser extent, Kim Il-sung. Even though the Cuban leader hitched his star to the Moscow, he was always a prickly subordinate throughout the Cold War and Cubans tended to push for a more revolutionary intervention in global politics than the more cautious Soviet leadership. So the USSR's leadership feared that if it did not intervene globally in support of what they saw as ideologically-correct movements, they could lose them to either rivals within the communist bloc, or the United States. The USSR did contend it was a global superpower and it did feel it had to act as one. These push-pull factors not only meant that the USSR would promote various political movements, it also conditioned which groups and actors it was willing to support. Sino-Soviet competition undergird Soviet support for North Vietnam, but the ascendancy of the PRC among the Khmer Rouge in Cambodia meant the USSR did not extend much support to Pol Pot.