So I decided it was about time to get the 30 threedeckers achievement, which I've been stalling on since I didn't want to be bored out of my mind playing GB in single player. However, I found a solution: to vassalize the world for the sake of enforcing pretty borders, and try to get as many of the blobs compose of rare countries as possible (Catalunya, Greece etc).
So far it's 1433 and I've just finished 30 years of constant war against France + Vassals, Scotland, Burgundy, Brabant, Aragon, Provence, Naples, Brittany, Bohemia, The Hansa, Luneburg, Magdeburg, Oldenburg, Riga, the Teutonic Order, Morocco, Karaman, Sweden, Styria, Switzerland, Avignon, Muscovy, and probably some other nations that I'm forgetting. Everyone DoWed me as soon as their truces were up (except Bohemia, but he couldn't find his way to France anyways so it didn't make a difference) and I nearly collapsed, with rebels occupying almost half my country and all of my mainland territory being occupied by enemies for the better part of it. I'd be dead if my initial high prestige from annexing half of France didn't let me sphere Friesland and then cancel the sphere to gain peace over and over.
Anyhow, I've accomplished something already (and which was why I had to enter thirty years of hell in the first place) which I'm relatively happy with. See if you can spot it (the above paragraphs should give some hints).