If you don't know about something, then you are not inclined to 'investigate' it and see what happened.
For instance, Custer's Last Stand has no particular 'relevance' to me.
But it was very interesting to visit the site, dig into it and learn how things get 'covered up', 'retold' and changed by people in power.
Without knowing about it, I would have never stopped and investigated the whole thing.
And if you 'open the kimono' you find Custer was not liked very much and the other two generals with him sort of said
"Hmm, Mr. Custer appears to be in trouble. We believe we'll just sit tight and defend our own position."
One particular bit of 'history' perspective sticks in mind from a personal experience.
Years ago, a lady attended our church whose husband had served in WWII in the Pacific.
She was in line at a local grocery store, and the lady behind was complaining that she hadn't heard from her husband in several weeks while he was involved in Desert Storm.
The lady smiled at her and replied 'Honey, my husband fought in WWII and I didn't hear from him for several years'.
History gives us perspective of a different way of viewing things.
Those who would try to frame moral choices and actions done years and years ago in terms of current 'morality' are either ignorant or intellectually dishonest.
We cannot comprehend the mindsets of those during the Revolutionary War, Civil War, WWI, WWII or the Korean War as it was a different time and different way of viewing things.
What we can do is learn from the bad choices and the good choices and try to profit from the experience.
But if we don't know then there is no profit to be had and we are poorer because of it.