The Great War undermined the Progressive agenda in relation to foreign affairs. Woodrow Wilson's vision of a rules-based international order had been a long-standing goal of the Progressive movement. Progressives wanted to see an end to imperialism; they wanted international relations to be conducted on the basis of cooperation and national self-determination. And although the United States's entry into the war was largely based on such principles, it paradoxically set back Progressive ideals in the formulation of American foreign policy.

Large sections of the American public were hostile to their government getting involved in constructing a new international system. It was one thing to fight a war to make the world safe for democracy; it was something entirely different to sort out other countries' problems for them. That was how isolationists in Congress saw the issue, and that's why they subsequently rejected the League of Nations. It would take another generation before the high-minded ideals of the Progressives once more became influential in the realm of foreign affairs.

WWI largely helped to end the Progressive Era. Government cooperated with industry in order to keep war materials flowing to the Allied Powers. The government insisted that workers not strike. This put an end to unionization efforts as many Americans viewed it as their patriotic duty to work toward defeating the Central Powers, whether on the battlefield or on the assembly line. After the war, there was fear of a Bolshevik takeover of the United States and this further hurt the image of unions as organized labor was seen as a threat to American democracy.

During the war it also became illegal to speak out against the government's war efforts. Eugene Debs was imprisoned for claiming that the United States joined WWI in order to secure industrialists' profits. Investigative pieces of journalism soon fell out of favor as the public wanted to hear stories of patriotism and heroism from the front lines.

The end of the war brought about a strong desire for "normalcy;" this was the byword which allowed Warren Harding to win the 1920 election. He helped get government out of the interests of big business; this was only accelerated under the Coolidge administration. The greatest legacy of the Progressive Era was the passage of the Volstead Act (Prohibition). Prohibition was initially considered a war measure as a way to punish German culture. It was also used to save grain for soldiers and Allied civilians overseas. After the war Prohibition was one of the few Progressive ideas that survived in the government, but it failed due to lack of enforcement resources and public apathy.

For the most part, World War I helped to undermine the Progressive agenda.

There are ways in which the war can be said to have advanced the Progressive agenda.  This is mainly the case because the war helped to bring about Prohibition.  It was easier for Prohibition to get passed into law because of the anti-German sentiment that arose around the war.  The biggest brewers in the United States were German immigrants and this helped to get people to equate alcohol with the enemy. 

However, the war did more to move Americans away from Progressivism than it did to promote that ideology.  By the early 1920s, Americans had grown weary of Progressive changes.  Historians argue that the war helped to make Americans want “normalcy” again.  Because of the disruptions of the war, people wanted to get back to a lifestyle that would be more relaxed.  Historians say that this included a loss of the sort of moral, reforming fervor that went along with Progressivism.

Thus, the Great War did more to undermine Progressivism than to move its agenda forward.