This question is a tough one because a good case can be made for each side. The opposite truth in each mode of thought is equally valid, making it a challenging question. In one respect, the United States did achieve its objective in entering World War I. It sought to stop the Central Forces. The United States was committed to stopping the Austrian- German alliance and render it useless. President Wilson was convinced of this threat as hindering democracy. The belief that Germany was able to facilitate an attack on the United States through Mexico helped to motivate President Wilson in his call to "make the world safe for democracy." This was interpreted as a call to stop Germany. The American presence in the war did this, essentially shutting down German advancement. Implicit in this is the idea that Wilson believed that German submarine warfare endangered the United States. He was able to parlay this into the idea that Germany posed a threat to democracies and fledgling democracies in Europe. Wilson's' commitment to stop Germany in World War I represents one aspect in which the United States achieved its objective.
It is here where the opposite truth is equally valid, thus making the question so challenging. President Wilson believed the war to be a moral one, a war that "would end all wars." His belief was that the focus of World War I was to end all other types of warfare with a fervor that underscored American commitment in it. This objective of the war as a "moral crusade" failed. The peace talks that led to the drafting of the Treaty of Versailles reflected this failure. President Wilson's commitment to see World War I as the "war to end all wars" was abruptly truncated when the presence of secret alliances still existed in the "peace" talks. Open acceptance of German reparations and a punitive judgment upon Germany essentially nullified Wilson's hope that World War I would be the final example of world conflict. The belief of "making the world safe for democracy" was undercut with a treaty that acted more like an armistice. Democracy was no more safe with the ending of the war than it was before it. The rise of the charismatic dictator in Italy, the Soviet Union, Spain, and Germany became the direct result that followed the end of World War I. Democracy was more under siege in this period than in the period that preceded World War I. It is here in which a very plausible case can be made that the United States failed to achieve its objective of idealism in the conclusion of World War I.