The Economist has constructed an index that attempts to predict where the next outbreak of unrest will take place.
This is a very interesting exercise. There are two aspects, one is the extent to which revolution can be predicted, the second is the assumption that a revolution will usher in democracy. The index only focuses on the first aspect.
The index "is the result of ascribing a weighting of 35% for the share of the population that is under 25; 15% for the number of years the government has been in power; 15% for both corruption and lack of democracy as measured by existing indices; 10% for GDP per person; 5% for an index of censorship and 5% for the absolute number of people younger than 25".
What the index is trying to measure is the level of dissatisfaction amongst people, hence GDP, corruption and a large youthful population. There are other factors as well and readers have suggested unemployment, inequality, the level of education, internet access, sectarian decomposition (countries where a sectarian majority is ruled by another minority), the degree of urbanisation and food prices.
All these are indisputably causes of dissatisfaction but the problem lies in their measurement and and weightage to be assigned in the index. Since these are somewhat arbitrary, the index may be regarded as an amusing intellectual exercise and perhaps a guide to wise rulers as to areas they need to work on to improve people's lives, rather than a sound predictor of revolutions. Nevertheless it is a useful reference point for someone wanting to study the issue.
One other factor that needs to be worked into this is the change in income levels and inequality over a period of time. If people have remained at the same level of poverty and there has been no change in inequality (ie the ratio between the rich and poor has not altered) then no additional dissatisfaction is likely to be caused, unless people's expectations change. The status quo has been maintained, the poor remain at the same level in both relative and absolute terms.
On the other hand, if living standards have fallen over time and/or the level of inequity has increased (the rich having grown much richer, or at least visibly richer), then dissatisfaction will grow. It is no coincidence that countries which have high levels of inequality (South Africa, Brazil) also have high levels of crime.
Assuming all of these factors are in place, the people will grow more restless and angry and a spark can set off a chain of protests that may snowball into a revolution.
Whether protest actually turns to revolution, depends on the ruthlessness with it is stifled and the extent to which the ruler retains the loyalty of the the army, ultimately the means by which a dictator's power is enforced (in a democracy power is enforced by a multitude of bodies). Therefore while a coup is a possibility, the success of peaceful protest is dependent on support from the army or from external forces except in instances where the ruler does not want a fight and flees.
Leaving aside the success of a revolution (measured in terms of ejecting its ruler) implementing democracy will be harder still.
Democracy is dependent on institutions and these need to be carefully built up over decades. There have been instances where it has taken root; Taiwan, South Korea, Portugal and Spain but in all these instances the despots were relatively enlightened and the people relatively prosperous. When the rulers saw a mountain of popular protest they decided to give in rather than murder people in the street.
In Spain, the King, who assumed temporary leadership after the death of Franco guided the introduction on democratic reforms. In Portugal's case it was a rather murky affair, a military coup followed by a series of tussles and elections, closer in spirit to the Arab revolts, that ushered in democracy.
The success rate for democracy has not been good. A series of revolutions across Africa in the late 1980's saw old-time strongmen deposed amidst great hope, only to result in a new set of of despots eventually gaining control. Only South Africa, with its established institutions avoided this fate.
I am not especially hopeful of the outcome of the current wave of revolutions, Tunisia looks the most hopeful and possibly Egypt.