867 start, figured I'd use hitting the 15 september 1066 mark to make an evaluation as to what has been going on so far
Starting of course with pictures
Firstly, pretty picture, I'm (obviously) the Persian Empire. A Zoroastrian ruler designer character based on Karen to be specific.
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And here's the current map of the world. Unfortunately several countries happened to have a civil war when I took the picture.
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I started with holy warring the Alavids (Shias, so the other Muslims didn't help them) and then got myself vassalized by the Samanids (Khiva). and ate their vassals from the inside. Meanwhile the Saffarids managed to conquer the rest of the Iranian rulers. So, instead of aiming to become king of Khiva and getting stuck between undesired Steppe lands and a large Sunni ruler, I went with declaring my independence from them via faction and signing up with the Saffarids to continue eating vassals over there for the next 40 years or so.
At that point several other vassals got a bit unruly so I decided to again go for independence and added a holy war for Birjand to that bit of disloyalty and from that point on quickly ate the remnants of the Saffarids and formed persia (Kingdom level) and removed all but one of the remaining independent countries between me and the Abassids before the Seljuks arrived. Who promptly decided it'd be a good idea to split their army in two groups so that they could quickly be wiped out. The only thing lost in that war was the thousand or so gold I was a bit overeager in investing on mercenaries

With the speedbump that was the Seljuks out of the way I could start joining the Byzantines in their race to devour as much as possible of the Caliph who, although having a slightly larger maximum army size than myself, was unable to do much against the combined forces of the Romans and Persians and around 1015 the Abassids were removed from the map with the Byzantines in control of Syria, most of Jerusalem and the northernmost duchy of the kingdom of Mesopotamia and me having taken over Mesopotamia and the duchy of Arabia. The rest of the Caliphate having declared independence to the point of removing the caliph from the map.
Following this came a period in which I expanded unopposed towards the south and along the African coast to the west. North of that I sometimes managed to take some land from Greek revolters along with fighting a few wars over small pieces of land with the Byzantines proper, sometimes with them having revolts and sometimes with them at full strength, the latter type of wars tended to be rather devastating to both of our countries' armies. Unsurprisingly considering they had the equivalent army size of the next 5 countries in line on the ledger (With the Persian Empire making up about half the army size of said five).
North of that we have some Tengri Turks whom I've left alone most of the time since I did not want to open up another race for land between myself and the Byzantines.
Just before the taking of these pictures I decided to let the Catholics know that they have a threat on the southern side of the Mediterranean and fought Francia, helped by East Francia and the Pope, for Menorca and followed that up by fighting Asturias for Seville and that is where I plan to further expand in the future.
Interesting notes about the other countries. Francia is elective and has most of the time been held by non-karolingians. Poland is Pomeranian. Ruthenia is Polish. Chud (North of Ruthenia) used to own Ruthenia as well and is Mordvin. England and Scotland are (reformed) Norse.