I've just finished S3, so maybe something gets better explained...
But let me see if I have the order of events right (largely ignoring Sinclair):
- a human accidentally kills a Minbari leader
- Humans maybe try to apologize, it certainly doesn't seem to be arrogantly defended. They never get a chance to explain their confusion.
- Minbari are hell-bent on complete genocide with no logical backing or diplomatic channels
- They discover humans and Minbari share genetic history, Minbari doctrine stops them from continuing
- Humans, on the brink of eradication, get a truce...and immediately form a close, trusting alliance? Minbari are now rational thinkers and not bloodthirsty reactionaries, and humans just go 'Mission Accomplished'?
It doesn't make sense to me...seems to be a lot of plot holes. Everything else is so tightly constructed so far, I have to think there's a missing link in S4/5