War-game a civil war situation. I don't think its possible against a modern state -- I was going to type out a few but they are so ridiculous -- they quickly end with the rabble being crushed by the US Military. Xinjiang is instructive here:

A geographically distinct area with a homogenous ethnic group distinct from the ruling class, with a distinct history and culture, with a strong separatist movement -- completely brought to heel by a modern state.