Seriously considering writing a timeline on an idea I have been playing with for the last couple of years. I have three P.o.Ds which occur.
The first P.o.D.
What if Richard the Lionheart of England dies in 1186 instead of his younger brother Geoffrey?
In this Alternate Time Line Geoffrey becomes King of England in 1189 when King Henry II dies (he died in 1189 in OTL). In order to keep John raising rebellion, Geoffrey sends him off to manage English territory in Ireland.
In a strategic move, Geoffrey sells (or just flat out gives) all of Southern France under English control (except for the border region with the Iberian peninsula) to King Phillip II of France. This allows England to do what it never could properly do in our timeline.
Plausible up to the point of "In a strategic move".
1) Aquitaine belongs to his mother, who is legally its duchess.
2) Aquitaine is part of France anyway, what is Philip selling? The dukedom (as in, the status of being duke)? Not his to sell. And this won't deal with Normandy, which Philip wants quite significantly - and which the Angevins have no reason to give up. The Angevins and Capets have problems to work out, though Philip presumably has less against Geoffrey personally than against Richard.
The Second P.o.D.
With the full support of English resources available to them, Aragon gains complete control of the Iberian peninsula somewhere between the years of 1195 and 1220.
The third P.o.D. takes place on the eastern side of the Mediterranean.
The full support? That's going to be tough to address plausibly on its own.
The Third P.o.D.
What if Alexios II Komnenos or Alexius II Comnenus Emperor of the Byzantine Empire managed to avoid being assassinated in 1183 and this led to the death of Andronicus Commenus who was the real voice behind the throne. Alexius II goes on to consolidate his power and position. As a result the Byzantine Empire is not plagued by in-fighting and tyrannical Princes and proves to be more successful than in OTL.
Any thoughts, comments, ideas, etc... that people want to share would be greatly appreciated.
Alexius is fourteen (in 1183), and not a very promising lad (when it comes to the perquisites of imperial government). But let's say he has some strong loyal supporters who don't see this as a chance to do what Andronicus did OTL. Stranger things have happened, so if you can find someone who meets this qualification (and please, don't just make up someone). Not sure where you'll find them - maybe the Lascaris or Vatazes families.
And of course, what was said about him as a kid may not mean very much (a young Achilles is not what you want in a ruler, especially a Byzantine one). Okay.
Obvious problems:
1) Hungary. Bela wants the stuff Manuel incorporated into the empire that "properly belongs" to Hungary on his side of the border. This is an easy enough deal to make and deal with satisfyingly, but it does need to be addressed. Not doing so may have another rival/enemy on the border, and the Byzantines don't need one.
2) Bulgaria is not feeling very happy about being part of the empire. This isn't beyond solution, but increased taxation might cause a rebellion like OTL. And you will need to collect taxes vigorously to afford dealing with the other eight problems - not necessarily more so here than anywhere else, but...
3) Serbia is independent in all but name, or full out independent, at this point. Yet another place to need to be reminded the emperor is in charge.
4) The Imperial bureaucracy needs some purging, if hopefully more gently than Andronicius did OTL. And the military aristocracy might need to be taken down a peg. You can guess how well this will go over.
5) Venice still remembers what Manuel did. This isn't dire, but it isn't helpful. If the massacre of the Latins has happened, that's going to be yet another tangle.
6) The HRE is a problem. A serious problem.
7) Did we mention the Seljuks are posing a problem to the Byzantine control of coastal and western Anatolia? This isn't good.
8) Norman Sicily.
9) The general exhaustion by overextension of the empire after Manuel I. It isn't beyond the empire's means to recover, but Alexius will need to move very skillfully to handle this and very patiently.
10) The Levant. So many problems. For starters, Saladin. And the prince of Antioch is Alexius's maternal uncle. And the succession to the kingdom of Jerusalem. And Cicilian Armenia (counted in with the Levant for convenience). And the Third Crusade is coming up, meaning Barbarossa will be entering the Empire by land. If this doesn't make you curse the Franks for ever inventing the ideas of crusade, you're going to do so by the time he's exited again. And that's if he behaves. And did we mention that Cyprus has a cousin of your father usurping control? Just for kicks and confusion? Yeah, it does. You can't even trust your own family.
11) None of these will wait while Alexius deals with any given problem. He has the decidedly enjoyable opportunity to face all ten things pretty much at once, and delaying any one thing will not make it easier.
It isn't impossible. But you'd need an unusually talented and lucky emperor to overcome them. And then there are the issues of getting married and leaving sons and all the mundane work of being emperor.
My timeline assumes an older Alexius who comes to the throne in a slightly better situation than OTL, so you might want to look at it (only done through to Barbarossa entering the principality of Antioch).
But all of these are very serious, and wrestling with them will to one extent or another use up Alexius's reign. And that's if he succeeds. Failure probably won't be quite as bad as OTL (1204 being a worse-than-it-should-have-been set of events), but it'll be more than bad enough.
But I strongly advise writing this timeline, even if it doesn't go as far as you hoped (Aragon not dominating Iberia, for instance) - its a good era for exploring alt-outcomes in multiple places.