Times Change, Once what was hatred between people , resolves with time. The primary occurrence of hatred is Jealously.
When people get jealous , they start taunting each other and then finally the fight breaks out which results in hatred.
Hatred occurs between siblings over competition and land disputes as well. With time these are resolved. There is a lot of ego, respect and dignity involved here wherein even if the hatred is gone, people wait for the other person to come and speak first to resolve the dispute and this prolongs the fight.
Point is to live and let live. Forgive and forget and live a peaceful life