is it ever justified to overthrow the government?

Fidel Castro, in the Havana Declarations makes the case that it is lawful and even a duty to overthrow a regime that is tyrannical

There is a lot of written material that support this position from the US declaration of independence to writings by Locke, Greeks and Roman philosophers, and even from Africa and Asia where it was the practice in some places to send to the maker a tyrant.

Why, then, do we have few insurrections when obviously we can count many countries living under a despot?