“Such men for the reasons given can open the way into the state and render the victory easy; but if you wish to hold it afterwards you meet with infinite difficulties.”

I learned this from the French barons who welcomed a foreign guest only to invite him in, thinking they could drive him out at pleasure. The conqueror gains the field by their help, yet loses the land when he tries to stay. You must crush them all or rule them as your own subjects, for half-measures breed endless rebellion that will eventually swallow you whole.