Detta avslöjas i serien såväl som i funktionsfilmen I början . (Egentligen den anledningen att inte titta på den innan du går igenom säsong 3. Det finns andra mindre spoilers för säsong 4 också, men det är inte så stort.)
More or less by accident during an interrogation the Minbari notice that Sinclair has the soul of Valen; that humans possess the souls of Minbari (and in this case not just some random Minbari after all!). Due to the law demanding that no Minbari shall kill another Minbari, they immediately surrender to uphold their ideals without having to tell anyone.
Vad gäller "varför en övergivelse?":
The actual "problem" here has been the fact, that the whole incident and the truth behind it (humans with Minbari souls) has been kept a secret by the religious caste, even inside the Minbari society. The warrior caste never really accepted nor understood the sudden surrender either and there are multiple occassions throughout the early seasons where Minbari soldiers clearly distrust Sinclair (and later Sheridan; especially for him being the "Star-Killer"). There are also several attempts by Minbari soldiers to create distrust between human and Minbari just for the sake of creating another conflict and continue the war.