As mentioned, the threat of Mutual Assured Destruction was enough to forestall the possibility of outright war; although one side or the other would have prevailed, depending on who fired their nuclear missiles first and who had the best anti-missile defense, there would have been massive radioactive fallout and probably retaliation as well as military reaction from other countries. Another factor was the increasing diplomatic relationship between the Soviet Union and the United States, which would define the political landscape for over fifty years.
The Berlin Blockade (1948-1949) was the first major conflict between the two superpowers after World War II; the USSR attempted to keep all support out of Berlin, to prevent help coming in from the Allies and by controlling supply, control the city. In response, the U.S. began airlifting supplies in and eventually were delivering more by plane than by train or truck, and the USSR had to remove their blockade in defeat. Because of the uneasy truce shared by the USSR and the U.S., the Soviets did not directly attack any of the airlifts, but instead used propaganda and harassment tactics to make delivery difficult. Despite air crashes and deaths, the airlifts were a success, and the USSR was forced to admit defeat and rescind the blockade. Again, direct military conflict would have been interpreted as a declaration of war by the U.S., and at the time it was not politically or militarily feasible.
Another factor, not expressly identified, is the increase in spying and espionage between the two nations. Despite political rhetoric, it would have been more beneficial to all parties for a covert, generally peaceful takeover, rather than a shooting war with many casualties, and this could have been achieved through covert operations, which would have been jeopardized by direct military action.