Historically over the past 100 years, if not led by military juntas, it happens only when a large group (thousands) of civilians in one area are literally starving or without electricity/clean water/heating fuel, and they have access to firearms. Either guns they own, or take from local law enforcement/military personnel.
Isolated pockets get put down, but if the problems persist on a widespread basis, SHTF. Soldiers begin deserting when they are ordered to open fire on starving women, elderly, and children, and things for the government get shaky. If military top brass decides that their own butts are on the line by resisting the uprising, it's over for the government.
We're probably a long way from there, but who knows? With the Neo-Marxists in charge and pushing as far as they can, maybe not.
