World War I had a profound impact on the progressive movement, and in many ways it brought the movement to an end. The war diverted the resources and attention of the American people from domestic issues to foreign affairs. The need to build up the military and fight the war took precedence over progressive reforms. Additionally, the war created a climate of fear and jingoism that made it difficult for progressives to advocate for their ideas.
The war also led to a rise in conservatism and a backlash against the progressive movement. Many Americans came to believe that the war had exposed the weaknesses of the American political system and that the country needed to return to a more traditional order. This backlash was reflected in the political victories of conservatives in the 1920s.
Finally, the war created a sense of disillusionment and frustration among many progressives. They had believed that their reforms could create a better world, but the war seemed to show that human progress was impossible. This loss of faith in progress further weakened the progressive movement.