Democracy has four fundamental components:
1. Political in primary purpose,
2. Population - based,
3. Internal to a single system of governance, &
4. Legal in form.

Revolutionary insurgency shares the same fundamental components, except the 4th is "illegal" in form.

Thus, the fundamental distinction between revolution and democracy is legality.

Most revolutions occur when trusted, certain and legal participation in governance is denied to all or some identity - based portion of the population.