I made all four of my kids watch it. My oldest 2 when they were about 16 & 17 years old, and my next 2 when they reached that age. Talked to them about it (the history) before we watched, then talked about the movie after we watched. Also, made it very clear that if they chose to never watch it again, that was perfectly ok. But they needed to see it at least once.
As a movie... IMO, one of the best ever made.... and the saddest.
Always brings to mind the old quote: "those who do not learn from history, are doomed to repeat it".