I had a high school teacher show us Threads during a breakout portion of 10th grade history where, for 9 weeks, you learned all about nuclear war. It has stuck with me my entire life. Somewhere about 2/3 of the way through the course we watched the film. It singlehandedly hammered into me what weeks of still imagery, theory, and historical facts could not.

What you learn most importantly from it is, while the initial hyper-violent effects of a proper nuclear war are so much more horrendous than anything humanity can imagine based on anything ever seen prior, it's the slowly diminishing quality of life that spirals out from it that reminds you of the futility and pointlessness of it all. When, ten years later, you see life is operating at medieval (or worse) levels, it's a truly crushing feeling.

The film is available on Amazon (for purchase only), I believe. Everyone should watch it, but I cannot emphasize enough that for some people it can be a real stressor. It has no happy ending.