So basically the game takes place in a post-post-apocalypic world. I can't really tell much without spoiling the lore, but the once advanced people now live in a chaotic world, fighting with blades and bows. There are quite a few factions, some are enemies, some are allies.
The game's lore is mostly hidden in books, but there are some unique characters that were alive during the 'collapses'.
The game itself is mostly fighting to survive, and later... well... what ever you want really. It is a sandbox after all.
If you want to know a bit more, just watch Sseth's video on Kenshi. It will help you understand better what I mean.
Also, though I'm not 100% sure, it's said that Kenshi 2 takes place before the second apocalypse, so there will be more lore once it's released. Not sure what I'll do then, but I feel like I should mention it.