That reminded me of the memoir of William Buckley.

( https://archive.org/details/lifeandadventur00morggoog/ )

He was transported to Australia in the 19th century, but thanks to a shipwreck he ended up joining an Aboriginal tribe. He was taught their language and joined their society to a certain degree (they thought he was dead, so a limited degree).

He was horrified by the level of violence in their lives, and sometimes when two sides were lined up to do battle he would appear and go around knocking the weapons out of their hands, which prevented the battle.

I like to imagine faux-outraged tribesmen loudly lamenting "Oh no, the ghost took my weapons! Obviously we can't have a battle now. Oh well, nothing to be done."