Comment by sfRattan

There's also The Lost Regiment[1] series, about a Maine regiment from the American Civil War transported to an alien planet. They discover that medieval Russian peasants were previously transported there and now live as serfs/peasants under nomadic alien warlords (IIRC the aliens periodically cull the humans for food). The Union boys, in tremendously fun if a bit predictable style, lead a peasant rebellion against the aliens.

[1] https://en.wikipedia.org/wiki/The_Lost_Regiment