Question

Why did the United States and the Soviet Union never go directly to war against each other?

Answer 1

Because the Soviet Union pretty much took over all of eastern europe.

They had the same goals: Spreading their chosen form of government to the rest of the world.

Answer 2

Adding to the answer above, the Warsaw Pact in Eastern Europe outnumbered Western forces in terms of manpower, tanks, and artillery. But perhaps the biggest deterrent were nukes.

By the fifties, the Soviets had proven that they could also build nukes. Still, if the Soviets simply steamrolled over Western Europe, NATO and its allies could retaliate with nukes, the Soviets would then do the same, and then that would be it. No one wanted to turn Europe, and then the rest of the world, into a radioactive wasteland.

As the years went on, both countries continued to stockpile nukes in the thousands. The Soviet Union, and now Russia, still have more nukes than the US does (based on rough estimates). You can see a few numbers here:

http://www.icanw.org/geography

As a result, both countries played a different game in the Cold War by finding allies in foreign countries, making alliances, espionage...all of the secret stuff to avoid having to shoot each other in the open because of the stakes.

Answer 3

There was never a sufficiently strong reason to do so. Neither coveted the other's land, and they do not share any borders, aside from the sea border between Alaska and Kamchatka. Both had strong interests in Europe, but the compromise of de facto division of Europe into East and West Europe was good enough to avert war. In fact, this division suited both countries to some extent, because it kept Europe somewhat prostrate and dependent, and prevented any additional intra-European wars such as the First and Second World Wars.

Bear in mind the presence of nuclear weapons meant that almost any serious war between the US and USSR could not have remained limited, but would have involved massive national destruction, with the deaths of tens of millions. That means both countries needed a very, very good reason to go to war -- something affecting the very survival of the nation. No such reason ever emerged.