Cathay (2001)

From the introduction:

Imperial Cathay is the largest cohesive nation in the Old World, with the longest continuous history of any human nation. However, it is not entirely ethnically so homogenous. It is largely Chinese in tone but incorporates areas of other East Asian countries, notably Thailand (Tialan) , Vietnam (Siewkang), Tibet (Kitsevara), and Korea (Han Kuo). Unlike the Old World, which is divided along ethnic and national boundaries, Cathay is largely a mixture of many different peoples, but ruled by one - the Li.