Since it seems the sort of clamor for a massive Total War mongol game has been steadily growing recently, I figured I'd sort of write out my thoughts on the optimal time period for a Mongol TW game orienting it around east asian history rather than the sort of typically european oriented history most people(understandably) have, which would IMO be the more optimal perspective to frame it from, especially since it would probably share the same engine as 3K and have a focus on East Asia in general. I will also just give some thoughts on how I would set up the game. Also I should say I make no pretensions of being a historian even as an amateur, though I'd say I am probably more knowledgeable of east asian, especially Chinese history than most typical english-speaking total war users are. But still, if I make any mistakes I can only apologize and correct them if anyone more knowledgable shows up.
Dimensions of the Map
Personally, I feel there could be quite a few ways they could do a mongol TW game. IMO, if they wanted there to be any sort of European involvement in the game they would have to make it a two-part game, in which case the European half of the game would sort of have a dual function as both Medieval 3 and the second(or potentially first, but I'd prefer second) half of a Mongol TW game. For the Asian half of this duology, I'd say that there are two main considerations: How far south it goes, and how far west it goes. IMO the most conservative map would be a map that only goes to the southern edge of china , perhaps including some of northern vietnam and as far west as the Caspian Sea, ending at the Zagros Mountains. So essentially you'd cut off Southeast Asia and most of India besides the Delhi Sultanate. IMO this map would work fine, however I personally feel it would be a missed oppurtunity, especially considering the exploits of some of the later Mongols like the invasions of Vietnam and Java by Kublai Khan. At the very least including the rest of Southeast Asia and India would be great both for the game and for TW, adding a lot of interesting countries, cultures, and importantly, sweet never before seen aeshetics in TW games for people to kill each other in. Maritime SEA might still be a bridge too far however, as to includ Java it would have to push the map very far south, though it could definitely be worth it. For the western edge of the map, IMO the Caspian Sea is a fine border, it would include the most important parts of Khwarezm which has at least recently become one of the more famous of the Mongol Conquests. It would be a bit awkward for the Golden Horde and Ilkhanate but you have to cut things somewhere, Extending further west to Mesopotamia would just leave the map feeling awkward, and pushing to the Mediterranean and Egypt/Anatolia is just way too big for one map IMO, especially since(unless they go for a very small scale for the map) this would already be one of the largest TW games ever. In the East there is the question of Japan, it's in a bit of an awkward position historically but IMO you might as well throw it in there.
IMO there are two main candidates for a starting date for TW: Mongol. First is the year 1205, or perhaps 1204 so certain things are not entirely locked in, which would be the year of the first Mongol Inavsion of Xia, and would set up the first pushes into Jurchen Jin. Either year starts with an already unified Mongol realm, primed for conquest. 1204 would just be before any hostilities start allowing a bit of freedom, but usually CA likes to have a starting enemy, which Xia would provide for the Mongols. The alternative would be a start some time in the 1190's when Temujin was fighting with Jamukha and the traditional nobility, but IMO I do not prefer this start, so I will assume the previous start.
Assuming a 1204-5 start, things could be quite an interesting time period in asia in general, and not just because of the incoming storm. In China, a rise in Song desire to reclaim the lost north from the Jurchen Jin dynasty, spearheaded by the statesmen Han Tuozhou who was essentially using the war as an attempt to save his political career would lead to a war breaking out in 1206. The Song had long been sort of basically blatantly funding insurgents in southern china, especially around the Shandong peninsula(that peninsula in the North China sea, where Kong Rong starts in 3K) and had also just been starting **** via border skirmishers for a while. Han Tuozhou ultimately had been preparing for war and was ready(or so he thought) for an all-out war against the Jin. Eventually this would lead to what Tuozhou wanted, a war, however things would not go as envisioned. Both empires would exhaust themselves fighting each other, though ultimately Song would be hit the hardest and have to reaffirm several humiliating treaties and tribute payments to the Jin by the end, though both empires were bloodied quite badly by the war, and with the Mongol Invasion only a few years away things were not good for Jin. In 1204, the question would be if you can conquer the north as the Song and succeed in Han Tuozhou's ambitions, or defend the border as Jin, hopefully at less of a cost so you can better fight against the impending Mongol Doom. IRL Han Touzhou would be executed, his head sent north to Jin as a peace offering. Ultimately this would be the last major Jin-Song war, though neither side really knew it at the time of signing the treaties to end it.
Tangut Xia would of course be basically screwed, I'm doubtful if you'd even be allowed to play as them though I think it'd be interesting if you could, but in any game where you are not playing as either the Mongols or the Xia the Xia should get wiped in like, 10 turns, tops. If you manage to avoid the Mongol onslaught though, your options could open up a bit, either to looking at whoever the winner is in the Jin-Song and pouncing. Xia was technically a Jin vassal, and in theory could expect Jin support in the wars to come, though it would like real life probably never come, and in game if they start losing it might be a good oppurtunity to try and get your own piece of the pie.
As a sort of "Fifth Bet" for China there would be the Kara Khitai. The Kara Khitai were centered around the Taklamakan desert and the trade cities of the Xiyu regions. They were descended from the Khitan Liao dynasty, a dynasty that had been ousted by the Jin about a century prior, but they had clawed their way back into some semblance of power by controlling the western regions. They were arguably, at least at the time of their exit from China, more sinified than the Jin ever were and even a century later chinese was still an important administrative language for the Khitans IIRC. Historically they would quickly be conquered on the way to Khwarezm by the Mongols, however perhaps you can turn the tides of fate and solidify your position and strike back into China, storming in and reclaiming your throne as the emperor of Great Liao, or perhaps you can instead push south into Khwarezm yourself and from there, India?
Korea I am not too familiar with. At the time they were ruled by the Goryeo dynasty, and were surprisingly competent, though still inevitably failed, in defending their realm from the Mongols. They were much like Xia a sort of quasi-vassal of the Jin, though I am unsure of how this would best be represented in game, and I do not think a direct vassal situation would really fit IMO. It could potentially work I guess. They'd certainly be an interesting faction, far weaker than the Jin though with potential to break out, or potential to sort of enter fortress mode and just try and defend against the Mongols until a later date.
Japan had just finished recently with it's famous Gempei War, and had only recently become a Shogunate. Sadly there isn't really any direct conflict at the start of the game to my knowledge, and it's definitely an interesting question of how Japan could be represented on the map at the start. While the Bakufu had risen, the Emperor would not go down without a fight and there would be quite a few attempts to break free, though not for a while yet. Some mechanic relating to this is a must IMO.
On the western edge of the map, the Khwarezmian empire had just in the year 1204 finally dealt the decisive blow against the Ghurid Dynasty solidifying their control(which we all know would of course be quite short lived) over the Ghurid's non-Indian territories. The Khwarezmshahs would basically only have one direction to go at first, though they could theoretically try and take on Kara-Khitai instead. I am unsure whether the Ghurids and Khwarezmian Empire should start off at war or not, they probably would still be in a state of war but since they just dealt that decisive blow it might be good to just have them really, really hate each other in game so a war can be started early but not necessarily immediately if neither side wants to pursue. In India, the Ghurids would very quickly get offed by one Qutb al-Din Aibak, a slave soldier who then took the reigns of the Indian territories, starting the Delhi Sultanate of India, specifically the period known as the Mamluk Sultanate. The Delhi Sultanate would go on to defend pretty valiantly against the Mongols, though they would eventually succumb to the mongol successor Timur who would utterly trash them while keeping them alive, and eventually their Mughal successors would finish the job and start their own empire. I am unclear on how the Delhi Sultanate should be handled really, maybe they can just bend history and have it be started two years earlier, or maybe it can be an event or something, I don't really know.
In Southeast Asia there were a few major states. No state was really strong enough to totally conquer everyone without getting invaded in turn, but that didn't stop them from trying. The main powers would be the Khmer Empire(Cambodia) which was probably the strongest empire in the region at the time and had the famous city of Angkor, which was one of the largest cities in the world at the time. Vietnam was split between the Champa states in the south(probably one faction in game) and Dai Viet in the north, which would quite impressively go on to defend against Kublai's mongols. They would usually fight both against the other, though occasionally Khmer would come in and they'd make alliances either against Khmer or Khmer would ally with one against the other. The Dali kingdom existed in the very far southwestern corner of china in Yunnan, and they are basically in the same exact territory as the Nanman are in 3K for reference. The Kingdom of Pagan would be the last major state here, which would be modern day Burma. They had a pretty famous battle in which the mongols got spooked by some elephants but managed to bounce back and defeat them.
And that concludes the post. Jesus that's a lot of text, if you read all of it, or even skimmed it, thank you! Tell me what you think, or don't.
I do have some thoughts on a setting for a Timurid Expansion, but for now I'll leave it at that.