How to be king when riding a horse and killing a war group

Join the army of a country first, and then lay down a number of big towns or castles at will. At this time, you ask your master to give you a city, but he won't do it, saying that you have already given it to others, so you choose not to agree and give up the oath of loyalty to him. Well, congratulations, there is another country called "XX Rebellion" on the mainland, and the king is you ~ ~

By the way, the premise is that you must have a reputation of several hundred points, swear allegiance to the monarch after you find it, and then go to the above steps, which is what I did.