"I agree. I was taught by English teachers too and the only times the US was mentioned when taking WW1, was when the mental crack the Germans got from the American entrance to the war was discussed, and of course the incompetence of some US commanders that got so many American's killed. Also the highly skilled marksmanship of US soldiers as a whole. But as the over all impact on the fighting and the war, it was always relatively small, which is as I found out later in life, was factually correct. But this is way off topic".
If you feel he is wrong then you might want to take it up with him.