A free mod for Mount & Blade II: Bannerlord, by yangraca.
This is a very simple application that upgrades a couple of units, which are called "Militia", from the vanilla game, to the "Veteran Militia" or "Militia Veteran". This change will allow you to upgrade your troops to a higher level, as you see fit, and they will not be useless anymore.
This application has 2 versions, which are called Vanilla Version and Plus Version.
In the Vanilla Version, all the units are equal to the ones already in the game, they just belong to a tree now of their respective names, so you can upgrade them.
In the Plus Version, you get some added troops to fill in the missing troop levels in the tree so you don't have to go from level 3 troop to a level 5. It's all done in the most lore-friendly way possible, with troops having skills they are supposed to have and items according to their respective kingdoms.
In addition to that, you get new items that you can use in the battle, called "Enchantment" and "Epicure". They will give you different benefits, like increasing your attack or defense, or increasing your health or mana.