Very often once things divide into the rich and the poor, there is decreased mobility and often the divide is along ethnic lines.  This increases tensions and reduces social cohesion.  The rich actually stop caring about the lower classes and then either they deny rights to the lower class (e.g. dictatorship, occupation, etc.) or the lower class elects people who take away richness from the upper class (e.g. socialism, revolution, etc.) -- either way it is a mess once the divide becomes entrenched and social cohesion breaks down.<p>One book that covers this well is World on Fire: <a href="https:&#x2F;&#x2F;www.amazon.ca&#x2F;World-Fire-Exporting-Democracy-Instability&#x2F;dp&#x2F;0385721862" rel="nofollow">https:&#x2F;&#x2F;www.amazon.ca&#x2F;World-Fire-Exporting-Democracy-Instabi...</a>