If you think of where the allies and axis stood relative to each other, it was very significant.

In 1917, Germany had already knocked Romania and Russia out of the war, allowing her to move millions of veteran soldiers off the Eastern front and to the west. Now, that doesn't mean she was about to overrun France, but it made it very unlikely that the UK and France were ever going to dislodge her from Belgium. That, in turn, makes it possible that, without US intervention, the UK and France might have agreed to a peace that would have preserved German power (though probably not her annexations).

Here, factor in the political ignorance of the Ludendorff-Hindenburg high staff, and the US contribution becomes paramount. Blind to the possibility of a political solution, convinced that Germany must retain her annexations in the east and secure Belgium and even French channel ports(!) for a greater Germany, they decided on launching a major offensive in Spring, 1918 before the US army could arrive in force. In other words, they acknowledged that the arrival of American forces would very likely tip the balance of the war against them. The March-November period of 1918 saw bitter fighting in which American forces participated heavily.

With or without American contributions it is unlikely the German high staff would have achieved their sprawling war goals, but the overwhelming American presence helped convince them to scurry for an armistice with their troops still in the field.