Mount & Blade II: Bannerlord

Using just your own troops, engage an army (composed of multiple characters and their troops) and win. You can tell the difference as a single person is called 'X's party', and a group is called 'X's Army' on the map.

My best advice is to track down an enemy army during a protracted war, where recruits and slim pickings. Stay out of range of it, and wait for them to be involved in a big battle or siege, leaving them with little to no troops, then swoop in once the odds are in your favor and attack them. This is best done with a trained army with around 150+ troops as I have come across several armies on their last legs with about 90+ troops available. I have found that it is best to have a trained all cavalry troop when engaging a bedraggled army as even if the troops count is close, you will often have a greater chance of winning due to your training & swiftness.