Empire Divided takes place during The Crisis of the Third Century. Want to learn more about this time period? Check this article out from Ancient.eu!
https://www.ancient.eu/Crisis_of_the_Third_Century/
"The Crisis of the Third Century (also known as the Imperial Crisis, 235-284 CE) was the period in the history of the Roman Empire during which it splintered into three separate political entities: the Gallic Empire, the Roman Empire, and the Palmyrene Empire."