Much can be said on this topic.

You are correct that learning from past mistakes should be a huge part of any history curricula.

I also find it useful to carefully instruct students of history to remain skeptical of historical accounts, because they rarely survive unscathed by bias.

Always assume the historian has an agenda, try to critically assess what that agenda might be, and consider the possible counterpoints.

The other challenge of history lies in the fact that we almost never have counterfactuals. That means we rarely can make truly definitive statements about historical causes and effects.

We do have a few significant natural experiments, like East and West Germany and North and South Korea.

By and large, though, I fear that we know far less than we think we do.