What events in europe led some americans to fear foreigners and foreign ideas after world war one?

There were several different events that made Americans fearful of foreigners and foreign ideas after World War I. The following are just a couple examples:

1) Russian Revolution- The overthrow of the Russian government and the newly created communist government scared Americans the most. This is because a communist system revolves around an enormous amount of government control. In a perfect communist system, the government would control how many products a business makes and how many resources a family would receive. This system allows for only a small amount of individual freedom.

2) German Revolution of 1918-1919