So, Zeniff's company left Zarahemla to try to re-colonize the city of Nephi. He was not the leader of the company at this time, he was just a spy. (The leader wasn't mentioned by name. I shall call him Bob.
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He returned to report to Bob to argue for making a treaty with them. Bob, being "austere" and "blood-thirsty" didn't like his argument and ordered Zeniff's execution. A fight ensued, and apparently Zeniff wasn't executed, although "the greater number" of the army was killed in the internal conflict.
As Zeniff himself later confessed in verse 10, he was duped by the king of the Lamanites into thinking they could live peacefully together. So my question is, if Bob had won the internal conflict, how would he have written about it? "I, Bob, had to put down a rebellion among my army because of a traitor that was fraternizing with the enemy and actively trying to deliver us into the Lamanites' hands." The winner gets to write the history books, right? Not that I'm trying to make any judgments on either side. It is true that they were eventually put into captivity, and many people died, because Zeniff wanted to spare whatever good it was that he saw. An ethical dilemma, to be sure. (And before anyone goes yapping about "imperialism," and how they should have stayed in Zarahemla, I must point out... the Lamanites willingly allowed this colony to exist. Zeniff didn't realize he was being duped, he was probably very excited in this new development in Nephite-Lamanite relations. Hindsight is 20/20. Insert political spin and/or aphorisms here.)