Province Strenght needed to conquer?

[Cohen]

I noticed it's common to use the pretender to early solo conquest.

I suppose a province is a big land, and if a lone unit can defeat an army, can take a lot of time chasing every routed unit that can supposely rally as guerrilla force, or to conquer small watch and guard tower there and there spreaded in the province, and so on.

I propose so to add a minimum strenght to conquer a province (like breaking a siege) after the battle and settle your ruleship.
There will be no further battles against indies in that province, and no "repairing" effect. Only time you need to plant a taxing system, send officiers there, and get it a sure land for supplying, retreats and so on.