.......When the Brahmanas became vegetarian, then it became the question for kings so as to which religion to support or patronize. It was essential because an irreligious king did not have much durability. One course was to patronize the religion which he got in heritance. The other course was to choose the religion which suited him best to further his territorial ambitions and which solidified his grip on the state. In this respect the Vedic religion scored heavily over the Buddhist religion. It provided direct divinity to kings. The Brahmans always extolled the virtues of kings who upheld dharma and performed Yagyas. They performed Rajsuya and Ashwamedha Yagyas for the welfare of kings while the Buddhist did not have any such concept. The Buddhism also eschewed the violence; the violence in fact was evident in the coercive power of the state. Thus Buddhism was not attractive to newly emerging kings because any violence was indispensable to formation of a new kingdom and a subsequent increase in its territory. However it was a god sent opportunity to Brahmans who were ever willing to grant Kshatriya status to new kings of obscure origin in return of land grants and plum postings with the kings and to save the dharma. And of course they used the performing of Yagyas as a mighty weapon. The Yagyas in themselves had a fascinating and a beneficial mystique around them. The kings who did not aspire to be Kshatriyas opted for Buddhism. The Buddhism automatically granted them Kshatriya status on the basis of presumed deeds of past lives. However their kingly ambitions suffered because of non-violence of Buddhism. Thus, the new kings were more oriented toward Vedic dharma and that ultimately led to its victory over Buddhism. There was a shifting of patronage towards Brahmanas. Over a period of time Vaisyas also shifted to Vedic religion to be on the safe side of the political powers. And after that Shudras also followed. There was a complete reversal to Hinduism. The Muslim invaders only destroyed the monasteries of a dying religion in north India.
However we find that by the time of Gupta kings, the Brahmanas had been successful in prohibiting the slaughter of cow - the divine and pure animal having pure excreta and pure urine. So they were the ultimate victors. It was made the most serious crime after the crime of killing a Brahman. The ploy of Brahmans of being deeply interested in the welfare of kings through performance of Yagyas paid rich dividends.
Now there is one more opinion that the Hindu caste system works like a division of labor. Everything is interdependent. Considering the level of agriculture available in Hindu society and its related ancient level of technology calling it a division of labor will be a misnomer. A real division of specialized labor requires a very advanced technology of multi stage production of different specialized goods that are required by most of the people.
However, it is better to call it a division of functions relating to a society which had a primitive level of agricultural technology. The Brahmans were engaged in intellectual and priestly work. The Kshatriyas were engaged in military and administrative work. The Vaisyas were engaged in business activities. The Shudras were engaged in doing labor activities. The untouchables were doing unclean jobs. Every body was supposed to be doing the job he was natural most suitable for – a great kind of dharmic harmony. On the face of it, it looks like scientific division of labor; the most suitable job goes to most suitable man. Only thing was that this suitability had to be acquired by birth. The status of a man also appeared to be job related. Higher was the job; higher was the status. The Brahmana doing the intellectual job got the highest status. The Shudra doing the blue-collar jobs had the lowest status among Varnas. The untouchables doing the lowest level unclean jobs got the lowest position in the society. This state where everybody is doing his divinely ordained function is also known as a cosmic order – with its all pervading divine harmony. But the question was how to maintain this cosmic order if Shudras aspired to become Kshatriyas and Brahmanas? If such aspirations of Shudras were realized then the cosmic order of the things would have broken down. The harmony was to get converted into disharmony with mere threat of demand for equality by Shudras. But how come the Shudras who were reciting Vedas and ruling over the people like Kshatriyas, would have been responsible for a break down in the cosmic order of pure and pious Sanatana dharma?.....