The need for the US to maintain a large standing army means that, inevitably, there will be heavy recruitment among immigrant Irish, Italians, Poles, and Jews into the lower ranks. To smooth out ethnic tensions (perhaps with the memory of the San Patricios of the First Mexican War in mind, men who defected to Mexico in protest of the war and of ethnoreligious discrimination by their WASP officers), that also implies that you'd want to draw some officers from their ranks--so you might see comparatively more of those groups represented among the officers, at least in the lower ranks. The US's alignment with the Central Powers might also lead them to imitate the Austro-Hungarian method of using the army as a sort of national school. Democratic Party political machines like Tammany might even find a way to use West Point admission as a party perk.
So New York and Illinois will also be picking up some of the slack.