there are inequalities in life chances between various categories of persons: male/female, black/white, citizen/foreigner, and so on. for each pair, you could attempt to give a pair-specific explanation of the inequality, something to do with its historical origins and how the inequality is persisting through time. what tilly is doing here is different: he is offering a *general* explanation that purports to cover all durable categorical inequalities. as you'd imagine, it's quite abstract. here in block-quote is one bit where he outlines the theory:

[begin quote]
Humans invented categorical inequality millennia ago and have applied it to a wide range of social situations. People establish systems of categorical inequality, however inadvertently, chiefly by means of these two causal mechanisms:

• Exploitation, which operates when powerful, connected people command resources from which they draw significantly increased returns by coordinating the effort of outsiders whom they exclude from the full value added by that effort.

• Opportunity hoarding, which operates when members of a categorically bounded network acquire access to a resource that is valuable, renewable, subject to monopoly, supportive of network activities, and enhanced by the network’s modus operandi. [...]

Two further mechanisms cement such arrangements in place:

• Emulation, the copying of established organizational models and/or the transplanting of existing social relations from one setting to another; and

• Adaptation, the elaboration of daily routines such as mutual aid, political influence, courtship, and information gathering on the basis of categorically unequal structures.

Exploitation and opportunity hoarding favor the installation of categorical inequality, while emulation and adaptation generalize its influence.
[end quote] ( )

http://bactra.org/weblog/algae-2013-05.html#tilly ( )

Tilly discusses social inequalities as being durable. He explains that through exploitation, opportunity hoarding, emulation, and adaptation specific categories in society are marginalized. Tilly seems to borrow ideas from Marx and Weber while integrating original thoughts. I would recommend this book to anyone interested in learning more about social inequality. ( )