The curmudgeonly lexicographer Ambrose Bierce defined history this way: "HISTORY, n. An account mostly false, of events mostly unimportant, which are brought about by rulers mostly knaves, and soldiers mostly fools."
The study of history can be an intensely frustrating pursuit. Recorded history is an incredibly complex collection of documents, millions upon millions of pieces of information. It's too much to learn in 100 lifetimes.
On the other hand, our records are incomplete, irretrievably biased in favor of the winners, and also strongly biased toward the deeds of the wealthy and the powerful.
Some say that we must study history so that we won't repeat past mistakes. I have seen no evidence that we truly learn from history, though. The same kinds of mistakes, atrocities and acts of kindness or self-sacrifice thread through the human story -- regardless of how well-read the actors are.
So, why study history? Despite it all, I believe that we do gain important perspective from history. It may not actually change our actions... but at least we can't say we were never warned.
Painting of Ambrose Bierce by J.H.E. Partington, Library of Congress Prints and Photos Collection.