> American kids rarely learn about most of the dozens of conflicts that have taken place since WWII, including the ones the US was involved in.

Added some emphasis.

Granted I graduated about 18 years ago, but my experience, and one shared by everyone I've talked to about it, including those who went to school in other states, was that our time in k-12 history classes were spent about like this (numbers ballparked but basically correct):

20% Early civilizations (largely "cradle of civilization" focuses, rarely going past the Greeks and not covering any of that remotely thoroughly).

25% The "Age of Exploration" in Europe and early American (as in, the continents) colonial history.

40% US history from about 1760-1900

15% Everything else. Probably half of our education of post-WWII material concerned the Civil Rights Movement, but it was very poorly contextualized and more of a "greatest hits" approach (as with most of the rest, really). World history post-WWII was hardly covered at all.

At the pace those classes move, there's hardly time to cover anything but the basics, and that only by leaving out huge swaths of time.

I only went into college with any significant grasp on history thanks to personal interest. It'd be entirely possible to have passed every grade k-12 with a perfect 4.0 and have huge blanks in one's historical knowledge. Most of the rest was presented with so little analysis and context that it was pretty useless (again, at the snail's pace those classes move, and with limited ability to push work on kids outside of class [especially, these days, for anything that's not math or reading] there's simply no way to cover very much in the first place, and none of it well)

A bunch of factors contribute to this, including:

1) You can only really push history so fast on kids under a certain age (go low enough and reading ability becomes a factor, plus they start with no context for any of this, and bootstrapping up to the point they can really appreciate what's going on takes a bunch of time). Most kids attend at least 13 total years of school by the time they graduate from high school, but they're only really receptive to a good history education for, at most, half that time—before that you're just trying to get them the building blocks to be able to understand stuff later, and often that doesn't even happen. This differential-ability-at-different-ages thing is why a curriculum will often repeat coverage of history material in multiple years.

2) We used to focus more narrowly on European history & heritage (and, broadly, the "Western" heritage of Rome and, by way of Rome, Greece), and put that stuff directly into things like the reading curriculum. It's no longer acceptable to have such a narrow focus and literature reading plans have shifted far away from that, leaving history classes to largely stand alone while the scope of what they're supposed to try to cover has only grown. On top of that, history classes are often less well-resourced than others (math and English classes, especially), notorious (especially at the high school level, where more serious history could be taught) as a haven for teachers who are mostly in the career to coach sports, likely to receive pushback from parents and admin if homework or reading load creeps above the bare minimum (that time is needed for math and English—if every subject gave out homework like those do, kids wouldn't have time to sleep), and constantly at risk of angering parents with facts (let alone even the tamest and most uncontroversial of analysis). Everything's set up for it to be neglected, and it is.