THE US HAD STAYED OUT OF THE GREAT WAR?

A prolonged conflict, a modified Treaty of Versailles and no League of Nations may have transpired without direct American involvement in WWI

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Although the United States had supported the Allied cause in the First World War with weapons, supplies and financial considerations, the introduction of American troops and other military assets in a direct role in 1917-18 was welcomed by the war-weary nations of Britain and France, and was an ominous development for Germany and the Central Powers. However, the absence of this US commitment to an active military role in the Great War may well have altered the outcome of the conflict along with the structure and steadiness of the tenuous peace that followed the armistice and the terms of the Treaty of Versailles.

How would the outcome of the Great War have been altered if the US had not entered the fight?

Clive Webb: Historians are not usually in the prediction business, not least when it concerns a future that never came to pass, and that may account for the lack of consensus about how US neutrality would have affected the outcome of the war. Some alternative histories have the Central Powers claiming victory. That would have led to Germany dictating peace terms that established it as the hegemonic power in Europe. Britain and France would've been ruined economically and unable to pay their debts, which in turn would've had ruinous consequences for their US creditors.