(Update: The account has been suspended.)
Q: why didn't the u.s. & the soviet union go to direct war?
Who says we didn't?
First, everyone was looking for peace and prosperity after WWI and WWII and the Great Depression.
Some of the growing animosity was vented through Proxy Wars. Technically, the USA was at war with Communist North Korea in the Korean War, but in reality the Soviet Union and Communist China provided the financing and raw materials.
As time went on hostilities grew, but by the time animosity had grown to the point where DIRECT war was likely, both sides had enough Nuclear Weapons to destroy the Earth several times over. The fear was that if war started, it would become Nuclear and both sides would lob everything they had in an attempt to ensure the other didn't survive.
This doctrine of "Mutually Assured Destruction" was the biggest barrier to outright war.
Side battles vented hostilities. The Space Race for example allowed both governments to "battle" each other without lobbing bombs. Vietnam was a bloody and violent proxy war.
There was also the philosophical problem. Both sides believed their own system was superior. While a military victory would provide relief from the government in question, it would NOT provide a total win in the face of the FORM of Government.
The fall of the Soviet Union was seen by many as the Death of Communism. The remaining Communist governments, like China, are slowly adopting a free market system. The economic defeat of Communism means it has little to no ongoing power.
This question has a high likelihood of getting me banned. It involves politics and I'm trying to remain level headed and fair. As this raving lunatic post reveals, being a member of a lunatic fringe is the way to ensure your questions remain intact on Yahoo Answers.