The name for this idea is "Domino Effect" - this is a theory that says that if one country falls to Communism the neighboring countries would also fall to Communism, much like pieces of Dominos fall when a neighboring piece fell.
This theory was important in the Foreign politics of the US during the cold war.
I would call this the 'Red Scare' as a phobia against communism or radical politics after WWI probably because the Soviet Union came out of WWI but on the contrary there were a lot of sympathizers to the cause of the Soviet Union and interest in their new experiment of actually trying to implement socialism at least among the Canadian and American working classes and many union members.
