For WWII from a historical perspective, I'd go with The Longest Day over Private Ryan. It gives a fairly even handed treatment for all of the combantants, not just USA. Tora, Tora, Tora is similar for Pearl Harbor.
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Why not just go with Pearl Harbor ????
She wanted world history, not fantasy.
Also a bit grim, but it shows the aftermath of the bombs dropped on Hiroshima and Nagasaki, there's a Japanese film (subtitled in English) called August Rain. If it helps, it has Richard Gere in it.
Would he be too young, or too bored by, Band of Brothers? It covers a lot of WW2 european locations and battle conditions, for all that it's primarily a character study of the men of Easy Company.
Likewise, From the Earth to the Moon (1998--I have no input on more recent versions) is more recent history, but if you're doing The Right Stuff, the miniseries hits a lot of that time period, too.
Kind of a very specific WWII topic, but I really enjoyed The Monuments Men.
Isn't World History going to be less about the 20th century and more about "ancient civilizations" around the world? What are the good movies about Ancient Egypt, Ancient Greece, China? How about the rise of Islam/Christianity? Medieval Europe and the Renaissance? Why can I not come up with titles for these topics?
Ooh, Mongol, I forget who it's by I think it's Russian. About Genghis Khan, very good. I honestly don't remember if it was subtitled or what.
Ooh, I don't think Spartacus has been mentioned, yet; or Cleopatra.
What are the good movies about Ancient Egypt
Unfortunately, all we seem to have are terrible flicks with white actors in brown-face with the background of video game violence. Or they are all about mummies and Egyptian curses, etc. The animated movie about Moses from the 1990s, "Prince of Egypt", was quite good, if I recall.
I think the best filmed material about antiquities are in TV series form. The HBO series "Rome" is fantastic but way too mature for a 15-year-old. And there is the splendid "I, Claudius" -- it's been ages since I watched it, but it's like 12-episode long and might be a bit dry for a high-schooler.