Once you've recruited a soldier, you can use them in battle to gain experience, which can then enable them to upgrade to better troop types. Regular troop types seem to be more favoured as the game progresses than any of the bandit classes, so consider raising troops from their respective factions rather than using a bandit force. You'll need to either buy recruits from settlements for a small amount of gold, or convert prisoners into troops after capturing them.
How to increase party size in Bannerlord.This Mount And Blade 2 Bannerlord troops guide will show you how to recruit troops, how to increase the party size, and how to command your troops in battle. Note that this is not to be confused with how to recruit Mount And Blade 2 Bannerlord companions, which is an entirely different process.
It'll take a lot of work, so we'll explain how to do it here. Keeping their loyalty, feeding them, and upgrading them to stronger troop types will be the key to conquering the land. Mount And Blade 2 Bannerlord has you commanding large armies in epic battles But first you're going to have to win them over.