The structural-demographic theory was developed by American sociologist Jack Goldstone (1953-) in the book Revolution and Rebellion in the Early Modern World (1991). This theory seeks to understand how, why, and when social upheavals like revolutions, rebellions, and protests happen. At first, Goldstone distinguishes between the causes (underlying structures and processes) and triggers (sudden events that immediately precede) of social unrest. While social triggers are either very hard or impossible to predict, causes are easier to observe and study, because they have a long duration and change slowly and predictably. Triggers, themselves are usually caused by structural factors.

The structural-demographic theory sees society as a complex system with three major subsystems: 1) the general population; 2) the elites; and 3) the state. All three subsystems interact with each other and with the fourth element – political instability – creating a „web of nonlinear feedbacks”. Changes in each of the four compartments induce dynamic change in other compartments. Also, each of the four compartments of the structural-demographic dynamic have their internal attributes or dimensions that influence structures and processes within each compartment.

The general population's most important dimensions are:

1. numbers - the size of the population and population growth patterns;
2. age structure -  the proportion of the whole population that is in each age group;
3. urbanization – the percentage of people living in cities and the rate of the growth of urban population;
4.  relative wages – median wages in GDP per capita;
5. social optimism – how people see their lives, government, and their future.

One example of internal dynamics of these dimensions is when relative wages rise it influences higher consumption levels, and higher social optimism, which all leads to increased social stability. On the other hand, rapid population growth can cause increased urbanization and instability in age structure and “youth bulges”, that is, large cohorts of young people that tend to introduce political instability (they are more susceptible to radicalization), higher unemployment, and lowering of wages. All these factors are intrinsically destabilizing.

The Elite consists of several dimensions:

1. numbers – the size of the elite, but also patterns of intra-generational and inter-generational mobility or closeness;
2. composition – the relative ratio of the proportion of established elites, aspirant elites, and counter-elites (radicalized aspirant elites);
3. incomes and wealth – share of national income and wealth attributed to elites;
4. conspicuous consumption – consumption of status-affirming goods;
5. social cooperation norms – norms that guide intra-elite behavior and cooperation;
6. intraelite competition/conflict – conflicts within the elite or between different elite segments.

The dimensions of the State are: 1) size, 2) revenues, 3) expenditures, 4) debt, and 5) legitimacy. The last compartment is instability, which is a process and not a social subsystem. Instability has dimensions of: 1) the “size” or frequency of minor instabilities (terrorism, riots) and major instabilities (revolutions and civil wars); cultural/ideological values (decline or growth of radical ideologies.

Other contributors to the structural-demographic theory are Peter Turchin, Andrey Korotayev, Leonid Grinin, and Sergey Nefedov.  

Reference:

Goldstone, Jack A. Revolution and Rebellion in the Early Modern World (1991);

Goldstone, Jack A. and Bert Useem.“Prison Riots as  Micro-Revolutions: An Extension of State-Centered Theories  of Revolution.” American Journal of Sociology (1999);    

Korotayev, A., J. Zinkina, S. Kobzeva, J. Bozhevolnov, D. Khaltourina, A. Malkov, and S. Malkov. „A Trap at the Escape from the Trap? Demographic-Structural Factors of Political Instability in Modern Africa and West Asia“, in Cliodynamics (2011).