In A Separate Peace what does this quote mean? "Wars were made instead by something ignorant in the human heart."

In this quote, Gene is pondering the events that occurred
during those crucial years at Devon school, and pairing it with his more mature
knowledge of war and people that he has gained throughout his lifetime.  Gene realizes
that he, in a symbolic sort of way, had declared war on Finny.  He ignorantly
concluded--because of his own insecurities and jealousy of Finny--that Finny was trying
to bring him down and distract him so that he wouldn't do well in his studies.  He
assumed that Finny always had people playing games simply so that Gene wouldn't do well
in school.  Finny struggled in school himself, so Gene concluded that Finny was
jealous.  It was that erroneous projection of his own jealousy that led to his reckless
actions at the tree.  He let his jealousy and ignorance guide his actions, and Finny
ended up with a broken leg. That event eventually leads to Finny's death.  So, Gene's
ignorance of Finny's pure intentions and true friendship was what, in the end, led to
Finny's death.

Compare that description to the quote you
related.  "War is made by something ignorant in the human heart."  Gene's heart was
ignorant--his own jealously led him to conclude that Finny was vindictive, when he was
not.  And that jealously led him to "declare war" on Finny in the tree.  Finny was a
casualty of that ignorance.  Gene takes that very personal experience and applies it to
war on a very large scale.  He concludes that wars are started out of that sort of
ignorance, not the larger, more sweeping evils that many people have often attributed it
to.

I hope that those thoughts help a bit; good
luck!