U.S. After WWI

      When WWI occurred many conflicts and tragedy's hit American lives. Americans began to have a fear against war, Fear of the consequences that happened after WWI. The economy was in a difficult state, returning soldiers faced  unemployment they took their old jobs away from women and minorities. Another consequences after WWI was the cost of living it doubled and farmers and factory workers suffered. One big fear that Americans faced were the spread of communism, with the spread communist would put an end to private property and many other factors that would affect the residents.
     With all the issues that Americans were facing they reacted and came with the idea of

U.S. used the technique of nativism to prevent war
against foreign-born people
Source 

nativism meaning, prejudice against foreign-born people. Another technique that the Americans adopted with the experience of WWI was isolationism known as being isolated away from the countries.
U.S. had fears regarding the League of Nations so, they decided to not care for others. They didn't know if they wanted collective security.
  The goals of the Communist during the war was to take full control over the people and make the country all the same  for everyone to have the same beliefs and the same rights.  

Communism became a fear to the U,S,
it was the concept that countries adopted in WW1
Source