Overview: A quick general history using the ideas of three major "castes" as a way of looking at how power is wielded and the consequences for society - concludes that governance is better wen all three are in balance.
Relevance: General background, interesting alternative to class as an explanation, I see some merit in the idea of people having different dispositions and that influencing how they behave in power. I used this as a vertical division on the diagram of hierarchies, classes and casts.