Progressives generally supported a Progressive president, Woodrow Wilson, in the war effort, especially after the war was cast as a form of idealistic progress, depicted as a way to make the world "safe for democracy" and as the "war to end all wars." After the war, however, a backlash set in: many Americans decided involvement in the war had been a mistake and retreated toward isolationism rather than the internationalism favored by Progressives. Also, the very fact that such a barbarous war had taken place between supposedly advanced and civilized nations brought about questioning of the whole idea of "progress." Further, a post-war economic boom in the US led to a more conservative, pro-business climate. The war was also followed by the establishment of immigration quotas aimed at curtailing immigration from certain countries. As immigrant exploitation was one of the causes animating the Progressives, the slowing of immigration shifted the emphases of the movement.
Conservatism surged after the war and Progressivism declined, but it never went away. Children's health, a Progressive concern, was an issue that World War I highlighted due to the number of malnourished young people who did not meet standards to enter the army. In 1921, the federal government passed the Sheppard-Towner Act, which, though modest in scope, was the first federally funded social welfare program. It provided federal matching grants to states and community organizations to build clinics to support women and infant health at a time when infant mortality was still quite high and childbirth was still the second leading cause of women's deaths. This paved the way for a goal cherished by Progressives: the idea that the federal government and not just states and local communities should provide for the social welfare of its citizens.
Prosperity, which brought high employment and wages, and a "Red Scare" brought on by the continued success of the recent Communist revolution in Russia also led to a decline in labor union membership in the 1920s. Since the Russian revolution erupted in response to the Czar's mismanagement of World War I, this was one of the ways the war affected Progressivism. The prosperity that dampened enthusiasm for unionizing was also, in part, a continuation of the production ramp-up begun during the war.
The Progressive Era is generally said to have ended with WWI. So the answer to your question would be that World War I essentially ended Progressivism.
After WWI, the US entered an era that is generally known as "the Roaring '20s" and is said to be the time when the country enjoyed a "return to normalcy." During the 1920s, the country moved away from the reform spirit that had motivated Progressivism. In place of that, there was simply a desire to have political peace and a desire to enjoy everyday life. These desires are said to have ended Progressivism.