From what I recall of the American history classes I took, we spent about a thousand years on the Revolutionary War (focused on ourselves, of course, without much talk of the outside help we got - Eddie Izzard wasn't actually joking when he tweaked the American audience in Dress to Kill for not knowing who General Lafayette was), some moderate time on our Civil War, stuff about the industrial revolution, and then we ran out of time at around the turn of the century. I had to get to college to take a class that covered any of our history after like 1910.

I did take a high school class that spent like a month on the Holocaust. (I was sixteen. We watched Night and Fog. I am still scarred.) It was my English class, not history class, bizarrely enough. So that was like, the only exception to the general "nothing from the twentieth century" rule that seemed to govern all history-related teachings.