Question

How did different aims cause tension between the USSR and the USA after WWII, leading up to the Cold War?

Answer 1

Both the USA and USSR also had very different ideologies. The USA and its western allies were for democracy. The USSR backed communism and a single party state under Stalin. While fighting the Nazis, both nations overlooked these differences against a common enemy. Afterwards, with nothing to really keep them to together, both began pursuing interests that favored their particular politics when it came to rebuilding Europe.

The US and the Western Allies were concerned over the independence of Eastern European nations like Poland which the Soviet Union had liberated. Soviet armies tended to stay put, so "liberation" in reference to the Soviets was akin to conquest.

Although the USSR promised elections and a policy that seemed to support their eventual withdrawal from those nations, they did the opposite which frustrated the West. Stalin was more concerned with taking what he could from Germany's former holdings to rebuild his own nation as well as setting up a series of buffers between Western Europe and the USSR. When elections or governments were formed in those nations, they were often made up of USSR sponsored allies.

It became a war of ideology, sometimes peppered with a little saber rattling on both sides, but would never break out into warfare (at least in a direct sense between the US and USSR). The split of Europe between East and West after WW2 was only the opening act in the Cold War.