Hans Castorp
Prince
Just completed it on Deity. The easiest way is to look for the cities that are never afflicted by Plague, since they don't lose loyalty and you don't have to buying Plague doctors to counteract it. For England, this makes it quite easy, since the Plague never reaches Dublin. All you have to do is build up Dublin, conquer Cork early, and keep your army there until the Plague loyalty penalty has robbed you of your English cities. These should all have a campus, which you can now pillage. Free cities are reasonably well defended, so you'll lose pillaging units, but it hardly takes more than 3-4 pillaged campuses to finish the game by this stage. A couple of caravels should have been doing the rounds to give you gold from harbours. For France and Castile, the redoubt would be Parma, which is less favourable, but easy to conquer. Haven't looked into Germany on Deity, but I suspect Copenhagen might be plague-free as well, in which case the strategy would work there, too. Alternatively, concentrate on keeping one or two decent cities loyal with plague doctors, cut the others free, and pillage as much as possible.