Okay, here's my try at assembling a general historical background for Interregnum, up to the start of the game. Its always good to get this kind of stuff organized (it may help things a lot to have a base to work from, and I will make very clear the parts I don't have straight. Unfortunately I have a hard time keeping my extremely awesome wit and opinions out of this, but later edits after certain things have become clear will slowly eliminate them. I probably missed a few regions as well. If I did, let me know.
1. KoJ: Does Jerusalem not fall to Saladin? I know that there was a lot of infighting in the Kingdom of Jerusalem which disunited it before Saladin reconquered it. While the Ilkhanate was at the borders of the Caliphate, the KoJ and the Abbasids joined up to defeat it at the borders of Baghdad, contrasting with when the Ilkhanate, to put it lightly, annihilated the great city in reality. Then they went back to rivalling each other, with some sort of uneasy peace until the player takes over.
2. France: The last king of France dies en-route to a crusade, I think besieging Constantinople (a siege which, unlike in reality, goes terribly awry for the crusaders). Because he didn't have an heir and Brittany declared that they would not be subject to another king who was not them, Burgundy, Brittany, and Savoie are elevated to the status of Kingdoms. The prince of Languedoc, I guess, agreed to put a stop to the Cathar heresy in his borders during the 13th century and thus doesn't have his lands divided up like they did by the King of France in reality. There is also Bourbonnais, Guyenne, Auvergne, Normandie, and Orleans as separate duchies, I guess. Lots of gray I need to be filled in on in all these categories.
3. England. Something happens to the King of England which causes the scots and welsh to pwn the English. It is divided up into York and Wessex (two and three provinces respectively), with Anglia to Normandie. Scotland has a lot in common with Norway and defends it against the evil eight-armed Kal(a)mari from Danemark and Sverige. Fill the world in here about what I left out, which was a lot.
4. Union of Kalmar. Sweden and Denmark form the Union of Kalmar, with Norway backing out in Interregnum, just before the game begins. The UoK is ruled from...guess...Kalmar, and gets into it quick with the Hanseatic League, which is German and English for The League League.
5. The Hanseatic League, which is either der Hanse or die Hanse, is, like the UoK, a recently-formed entity in this game which is comprised of united mercantile city-states. In the beginning of the game it is fighting for its independence, which is not a worry because it comes to be about five days after the game begins.
6. Cordoba. Due to the division of France, the northern parts of al-Andalus are not able to be backed up by a powerful entity and thus cannot reconquista back. Cordoba never falls to the Castilians and thus doesn't lose its important status to Gharnata in the south. In 1419 there are three iberian states which will almost invariably lose to Cordoba--Porto, Galicia, and Leon. If the other two christian iberian states don't exist and the third has over seven provinces (IIRC), then it gets to form the Christian Kingdom of Asturias. This means that Cordoba is losing the Reconquista. I have another question here, btw--how would the acceptance of the Iberians under the shepherd king affect the language of the cordobans? In times of trouble, such as plagues, the ruling classes start speaking the common language suddenly. Not that Norman French is a particularily important language in religion, but were it not for the Black Death the aristocracy of England would not have started speaking the language of the peasantry, which they did. Just because the people of, say, Madrid, once converted to Mu'tazelism are andalucianized doesn't mean that people will start speaking arabic in everyday life. They may (certainly) would adopt the arabic script, but they would still speak some sort of Castilian (anyone ever wonder about the similarity between the article el and the I-don't-know-what-to-call-it al?) For example, "El Rey Don Pedro el Cruel," King Peter the Cruel, could be rendered as something like "Don Pedru el-Kruwwel el-Rey"..."Dn Bdru (e)l-Krwwl (e)l-Ry," if you are so inclined. Not that such a character exists in this timeline. Just throwing something out there; it really has a place in a different thread, like the Cordoba one. Anyways, just some flavor.
7. Germany. The Bavarian House Wittelsbach has, due to the crusade which killed the king of France and a lot of German (and Dutch) Princes, inherited a lot of land from said deceased monarchs. In addition, they are also the Holy Roman Emperor, and its a good idea to try to keep the title, just as it is good to win the crusade against Cordoba.
8. Russia. Muskovy never rose to power, and Novogorod is in the power of the Hanseatic League. The Russian states are Suzdal, Tver, and Ryazan.
9. Finland. The Scandinavians who tried to convert Finland to catholicism were only able to get Abo, the actual Finland province. So, Finland is Orthodox, because the Orthodox missionaries presumably didn't try to do it down the shaft of an arrow.
10. The Golden Horde is, just like in reality, really annoying to play because of all the anarchy. However, it is rewarding, with the opportunity to do something freaky and convert to Buddhism in the middle of the game, though there isn't much to do outside the realm. History here, as far as I know, isn't any different from real world history. Though if Temur never got power in the western Chaghatai Khanate, he wasn't there to overthrow the Khan of the Golden Horde who tried to (and failed miserably to) screw with his empire. Off the top of my head, I think the Khan may have been named Jahangir. Probably not, though. Anarchy happened all the time in the Golden Horde, so that doesn't really matter.
11. The Baltic. As is apparent upon first loading the game, the Teutonic Order reigns supreme over most of the Baltic. Apparently they conquered Lithuania instead of sitting around letting it convert to Catholicism. Because of this, the three Lithuanian provinces are pagan. Also, the TO has a desire to mess around in Poland. However, in Poland's place and having something like the strength of Poland is Halych-Volhynia.
12. Halych-Volhynia/Ukraine. Rivals, something like the KoJ and the Abbasids. Its religious too, with HV catholic and Cossack Hetmanate and Kiiv Orthodox (and Kiiv usually gets eaten up by HV and/or CH early). If either conquers the other they gain the cores and probably the right to be called Ruthenia. As Constantinople hasn't fallen, I move on to the next set.
13. Roman Empire. (BTW, I petition that the Byzantine Empire gets renamed to Roman Empire)At some battle or other, the unusually lucky Byzantine army soundly defeats the turks, forstalling their advance into Constantinopolis (city name-change petition!). By forstall I mean that Teke or Karaman usually makes it all the way to the edge of Anatolia within a hundred years, no matter how strong Byzantium is. They have quite a few paths and far far more leaders than other kingdoms, probably leftover from Abberation though these names can be used for other things if so desired. Yes, I just thought of that, which is good.
14. Swabia is the Hapsburgs who were unable to acquire Austria from Bohemia. They get a chance to inherit Milan near the turn of the 16th century, which disappointingly almost always goes to Orleans.
15. The New World. The Maya are based in the Caribbean sea rather than the Yucatan peninsula, which is quite possibly a good historical possibility. The Zapotec quickly control all of Mexico. The "Inca" have been split up to be more historically accurate, and also a country called Wanker is included down there. Some people like to play with Wanker and make it grow and stretch across and between all the mountain peaks of the andes, and to the dryest or most frigid places on that continent. But not me.
16. India. India has been divided up into four different countries--Sindh, Chayuluka, Chola, and Lanka. And another one, which I forgot. Either Calipah or Ahmad was working on this region, and i have no idea why it got split up like this. There is still a lot of room for work here, though there is everywhere.
17. China. China has been split up into five different entities, two orthodox/nestorian Christian (one called Mongolia) and the others Confucian. I don't remember the rationale for this, if I ever read it, and some explanation would be cool. I think Ahmad wrote some stuff about it in a really long thread. Unfortunately what he wrote was based on a Muslim northern India (IE Bengal), which makes it a little hard to deal with.
18. Siberia. Empty. Don't have any colonizers as of yet, or a Mongolia which lives in the siberian corridor; it all ends at pagan Sibir Khanate.
19. Ilkhanate. As it seems that Temur never built his empire in our game, the Ilkhanate still exists and is ruled by Hulagu III at the start of the game. This Khanate is Buddhist mostly, though its Iran (yes, Iran. Not Persia) is mostly Muslim. It has a Nestorian vassal called Qarluk on the eastern Caspian Sea. Its biggest enemy is the Caliphate.