Dr.Ambedkar in Annihilation of Caste:

It is a pity that [tag]Caste[/tag] even today has its defenders. The defences are many. It is defended on the ground that the [tag]Caste System[/tag] is but another name for division of labour and if division of labour is a necessary feature of every civilized society then it is argued that there is nothing wrong in the Caste System. Now the first thing is to be urged against this view is that Caste System is not merely [tag]division of labour[/tag]. It is also a division of labourers.

Civilized society undoubtedly needs division of labour. But in no civilized society is division of labour accompanied by this unnatural division of labourers into watertight compartments. Caste System is not merely a division of labourers which is quite different from division of labour—it is an hierarchy in which the divisions of labourers are graded one above the other. In no other country is the division of labour accompanied by this gradation of labourers. There is also a third point of criticism against this view of the Caste System. This division of labour is not spontaneous; it is not based on natural aptitudes. Social and individual efficiency requires us to develop the capacity of an individual to the point of competency to choose and to make his own career. This principle is violated in the Caste System in so far as it involves an attempt to appoint tasks to individuals in advance, selected not on the basis of trained original capacities, but on that of the social status of the parents. Looked at from another point of view this stratification of occupations which is the result of the Caste System is positively pernicious. Industry is never static. It undergoes rapid and abrupt changes. With such changes an individual must be free to change his occupation. Without such freedom to adjust himself to changing circumstances it would be impossible for him to gain his livelihood

 i wonder if the division of laborers, over the centuries is what led to so many conquests…. i also wonder whether it was this division of labour that led to a dark ages where there was no social, scientific or technical progress. 

I often wondered how 3% of the population was able to the bulk of the population subjugated for so long. Why was there never a revolution. The answer was quite simple, they didn't have to do too much. The zillion odd castes kept each other in check and ensured that the system thrived at the expense of everything else.