The period of disunion from 311 to 589 CE saw the territories of the former Han Empire (206 BCE–220 CE) carved up into as many as twelve contemporaneous states ruled by a tumultuous succession of some forty different bloodlines, the majority of which were ‘barbarian’ in origin. As it happens, this was also one of the most fruitful periods in the history of Chinese-language astronomy and mathematics. Experts were divided, working on the same problems in rival capitals, increasingly disconnected in written and oral tradition except as punctuated by violent redistributions of human and material resources by invading armies. If ever there were a place and time to go looking for 'different mathematical cultures’ in early imperial China (Chemla 2009; 2016; 2017a; 2017b; Zhu Yiwen 2016), these 278 years are it. Catering to this particular mission of the SAW Project, this paper will break the history of astronomy and mathematics in this period into that of four distinct regional networks, between which we can effectively divide more than a dozen received texts and what we know of many more that have not survived in full. Grounding our sources in their immediate geopolitical and interpersonal context, this paper will argue that the dividing lines between regional traditions is often stronger than those between genres of mathematics within li 曆 and suan 筭.