The Origins Of Revolution

Lucan Way contemplates them:

Ties to revolutionary struggle give military and security officials a sense of mission required to engage in risky and violent behaviour necessary to put down large scale protest. In Iran in 2009, the legacy of 1979 ensured the loyalty of a powerful, and ideologically motivated coercive apparatus that was able to put down a serious opposition challenge.

By contrast, regimes rooted mostly in patronage - such as Egypt, Libya, and Tunisia - are much more vulnerable to crisis.

When-due to economic downturn, widespread protest, or a strong electoral challenge--the ruling coalition's hold on power is threatened, regimes that are bound together primarily by patronage often suffer large-scale defection. Indeed, if a crisis convinces ruling elites that continued loyalty threatens their future access to patronage, it may trigger a bandwagoning effect in which politicians defect en masse to the opposition. As one defecting member of the ruling UNIP party in Zambia that collapsed in 1991 put it, "only a stupid fly ... follows a dead body to the grave."