i don't know your feelings on this so please understand i'm not trying to argue.
the answer is part of a different problem which lies in teachers unions specifically tenure. if there are no consequences for your actions what is the incentive to do a good job? when i was in school i watched a teacher pound a kid's head into his desk repeatedly (the kid, about 12 years old, asked for help on an grammar question), ram a kid into a locker until he laid on the ground crying (he was about 14 years old), and i had a teacher on my lunch tell me he was going to "take you to the parking lot and teach you a special lesson".. my offence was talking to my friends at lunch about a model bridge we had to build for the next class. i was 14. as much as i don't want to admit it i have more examples. none of those teachers faced any disciplinary actions (all of the teachers were tenured) and in some cases the student got in trouble (the kid rammed into the locker got a 1 day suspension for it)
so i said that to say this.. since ww2 is more popular in the u.s. than ww1 and teachers, in general, find it more interesting.. they will teach what they want to teach.
please don't get the wrong idea i had good teachers too. most teachers were there to get their paycheck. they weren't good or bad they were just there. it's the bad ones that formed my opinion that teaching children is too important to have tenure. (i'm still on the fence on if teachers should have a union at all and i'm not anti-union)