I haven't posted anything on this yet, but a mod like this looks too good to be true. I am a historical freak, which is why i love civilization colonization, so i want to add my two cents to this conversation.
Personally, I think the game should start around 1421, which is supposedly when Zheng He could have possibly discovered america. I know this game takes place in asia, but the fact that the chinese made it to america demonstrates that they had the capabilities to colonize in the pacific if they had the right incentive.
As to what civilizations should be included in this mod, i would want to see the ming dyanasty (china), Japan (as represented by Tokogawa and Nobunka as seperate leaders), the Vijayanagar (southern Indian nation at this time period: it reached into indochina and a little bit into indonesia), and finally the Portuguese.
these four nations had the most power in the period between 1421-1500 and 1500-1792, these four nations had the resources, manpower, technology, and inovative skills to colonize the east; unlike the others you guys had mentioned. The mongols never became a sea power (except invasion of Japan, failure) and by this time in history the mongols had reverted to their previous way of life: herding and being nomads. The mongols at this time are much more like the native amerians of the the new world. which brings me to my third point:
the mongols, tibet, kmer empire, indonesia, and northern indian states should be like the native americans in this colonization where they have single city borders, limited diplomacy, and no cohesive resistance against colonization. This leaves the islands of the pacific, indochina, and central asia and northern india up for colonization to all the major powers. (by the way, you could add enlish and french to the mix, although they didn't become serious players in this part of the world until the eighteenth centuries.)
And to better represent the asain countries i would like to pose an idea. to represent the overpopulation of the asian nations (specifically india and china) why not put a restriction on their industry? give them the ability to harvest twice as much raw recources ( like tobacco, cotton, and sugar) but make their industrial buildings like twice as much production points. this would represent how these powers could harvest alot of materials because of their large manpower, but penalize them for their lack of industry; this would almost balance the two off, but allow a small advantage to the european powers, particulary portugal. I would also add a benefit for the portuguese giving them extra traveling speed on their ships and extra attack to represent their far flung asian empire.
For game dynamics, instead of just destroying mongolian or indian cities like with the native americans in regular colonization, alow the player to choose to destroy it or keep it. Like how the portuguese held on to gao for centuries, while they also destroyed societies when they took over a few islands in the indonesia. Also, give the asian powers greater ability to make more units (half production value to build?) but make european units a few points stronger to represent the asian powers ability to wage a decent war in this period. I hope this wasn't too off from what you guys were thinking and i hope this helps in some way.
