The correct answer to this open question is the following.
The three ways in which the attitudes of the United States changed after World War I from what they were before the war, were the following: America lost interest in progressive causes, Americans wanted to return to a normal lifestyle, and the question of isolationism or internationalism was a major concern.
President Woodrow Wilson firmly thought that the foreign policy of isolation was the best for the United States. That changed when the United States intelligence intercepted the Zimmerman telegram where Germany asked Mexico for help in World War I, and then, the sinking of the Lusitania ship by the German Navy. The United States entered World War 1 on April 6, 1917.
After those years of conflict, the citizens of the United States did not want more economic restrictions, no more soldiers' death, more peace in their lives, and demanded the US to stay away from international conflicts.