All these wars included rape, plunder and carrying away of the loot which included maidens also. Many of the old kingdoms did not have "standing armies", meaning soldiers on a regular pay and in army barracks. At least this was the practice in most of south India. Even in Tamil Nadu, when the king declared war, the fact was announced throughout the land and all able-bodied men (excluding brahmins, of course) were conscripted. If these soldiers returned from the war victorious, they could usually keep all that each of them had looted from the enemy territory and also any cattle & maiden whom he had carried, subject, of course, to first charge of the king and the army commander/s.
Hence, it will be observed that there used to be "varna samkara" (as Arjuna fears in BG) in many instances of the common population but climbing up the varna vyavastha was not possible; it was mostly one of going down the ladder.
The "king" irrespective of the caste/varna to which he originally belonged (before acquiring his first small kingdom) usually acquired the "kshatriya" status with the patronage of brahmins. I have read that even the Naiks of Madurai thus got a kshatriya lineage from king Mahabali or someone.
Therefore, the general rule in Hinduism has been that one's varna or caste is determined by his birth and is unalterable; the examples given above are the exceptions.
"veLLALar" (water - veLLam) were farmers who were probably experts in irrigation of rice fields and "kARALars" (kAR = cloud, therefore, rains) had gained some expertise in predicting the rainfall pattern; both belonged to the vaisya category at one point of time. Therefore "vELAn cheTTi" may not have been really a change of varna but only a sub-caste within vELAn, a farmer with certain typical land right over his cultivated lands, like அரையன், பேரையன், உடையான், நாடாழ்வன், மூவேந்த வேளான், etc. (
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