Sorry, can you explain it a bit better?
All nations act in their own perceived self-interests - or at least, their leaders' perceived self-interests. The first of these self-interests is survival - all nations wish to survive. There are a few exception to this, but only in situations like that of Kosovo, where a nation actually wants to be part of a greater whole. Very rare.
The second is the pursuit of power. This is related to survival, because the more power one has the more likely one is to survive. Survival is by far the more important of the two though, which is why certain states have intentionally limited their own power in history - a good example is Bismarck's refusal to take territory from Austria at the end of the Six Weeks' War - in order to avoid an alliance against them.
The USSR's actions in the Cold War were motivated first by survival, then by power. There was also an ideological component, but this was secondary. After all, Russia routinely supported groups that actively opposed communists to the point of slaughtering them, such as the Kuomintang in China. The USSR took control of Eastern Europe in order to have a buffer zone between itself and any subsequent Western assault, understandably so, considering the war with Germany. It also took more territory it didn't need, such as Albania, because it increased their power, but it was willing to let these territories leave its sphere as they were no threat. Austria's another example.
The USSR's actions in the Third World were motivated by similar concerns. Stalin intentionally stayed out of the Middle East after the Iranian adventure in order to avoid antagonising the much stronger US, but his successors quickly seized the opportunity to gain allies from among the disgruntled Arab states in the area, Egypt most of all. This policy was based on ensuring Russian access to resources, in much the same way that the US and Britain interfered in the Middle East to gain resources. They did the same throughout Africa, Asia, and when the opportunity presented itself, Latin America. They were not doing this to seek world domination, but simply for their own survival and to protect and expand their interests.
Now, if a state actually had a chance of achieving world domination, they might take it. But not if the risks outweighed the rewards. The Mongols are a good example, they stopped their conquests when the risks of continued expansion and warfare outweighed the potential benefits.
