The fact of the matter is that the Great War, was also the first World War in that sense the outcome was dictated not on the fields of flanders, but rather in the governments of nations across the world.
The OP is rather vague in what it means with 'without America', since that can be taken to mean anything from total isolationism, no trade, some trade, select trade, equal trade, free trade, no political support, some political support, select political support, non involvement, some involvement etc. the list goes on.
The fact that the First World War was so large in scope was partly to blame for why it transended a local conflict and came in its very nature to shape international relations, and why the United States were eventually drawn into the conflict. Americas interests still being myriad in the 'Old World' and the ties that bind are not so easily cut.
Which means which ties could be plausibly cut in the zietguiest of that period?
Let us go back to 1913 before War in Europe was on the cards, there was no federal bank or income tax in America. In 1907 there had been a banking panic, so Americas position before the Great War was less than stable. This in my opinion is the best place to start for looking at a Point of Divergance in American foreign policy and internal affairs.
The question being how much stink could the writting of the 16th Amendment create within the US so that by the type Princip kills of Franz Ferdinand the US is more worried with its own internal problems than that of what is going down across the atlantic.
In such a POD if the American government is delayed forming an opinion on the European war, and the US markets are sufficency cautious due to economic instability in the US and across the atlantic that trade itself is not occuring, then you have a way for butterflying out US involvement in the conflict before the Etentent have had their big faceoff with the Central Powers. In such a case US involvement would come too late, and as such a Great War without American involvement.