If someone who is able would be willing to make a map (note it doesn't have to be that big in scale) that would be great.
If people insist on using the same nations they use in modern taijitu and/or the map we use in modern taijitu I have a solution, if prior to the history that has already been agreed on we say that there was civilization prior to that but that it was destroyed by some form of massive natural event (or anything we could even say that they got up to the nuclear stage and used them) like a comet/asteroid strike, super volcano or what ever which destroyed these civilizations and reduced humanity to the brink of extinction (which has happened in the past (the reduced to the brink not the civilization thing to the best of my knowledge)) and then humanity recovered to reach the world we have today.