The phrase that “those who don't learn from the past are condemned to repeat it” is one of those clichés that provides the "illusion" of being a useful piece of advice, especially when what we're going through now seems “just like” back then.
Umm… no.
Historians who study the use of analogies in policymaking warn us against saying that two situations are alike without considering areas where they are markedly different. Historical reflection guides us, but as a challenging discipline rather than us “learning” the answer.
Moreover, it's good to compare the current situation with several alternatives from other parts of the world and other time periods. So, if we want to make a comparison with the U.S. Civil War, for example, try opening the aperture to include perhaps the Russian Civil War or the English Civil War or the Chinese Civil War or perhaps even the tensions between the Paris Commune and the Third French Republic. Different interpretations may even point to different lessons from the same example, depending on whether they saw themselves, in this case, on the winning or losing side of the given civil war. So, we see that history is not some unchanging list of “lessons” that we can just apply to our current situation.
History was and is messy and so learning from the past starts with embracing that messiness… and then there is the parallel cliché that learning from the past frees us to make brand new mistakes.