The deep rooted animosity between Vellalars and Nadars from 15th century in Tirunelveli regions and how Vellalars rose up in hierarchy and pushed the Nadar community to the fringes, is explained in this article.
http://sishri.org/Deccan.html 

For example in an inscription dated 1453AD titled 'Kallidaikurchi Thaikatheru Kalvettu', it imposes a ban on the Vellai Nadars from re-establishing their kingdom taking the help of other communities like the vellalas who till then had a subordinate position in the Nadar courts.

It was proclaimed by the assembly of Vellalas, to put to death the Vellai Nadan violators, namely, Kolari (kalari) Ayyappan, Ayyan Kumaran, and Andur Chezhiyan, for marrying females of Vellalas.

Another interesting news, is that Nadar's right to temple entry was questioned by Vellalas who occupied administrative posts in the temple oriented social setup in the 19th century.

In the year 1872, concerning the entry of Nadars into the Tiruchendur Murugan temple, Vellalas filed a suit in the Srivaikuntam court (case number 88 of 1872). The contention of Vellalas was that Nadars must be prohibited from entering the temple as they belonged to a low caste.

In that case, Aiyasamy Dikshithar of the Pasur Mutt (Salem district), kula guru of Kongu Nadar community, appeared in the court and testified that the Nadars belonged to the Pandiya kula Kshatriya lineage. The decree went in favor of the Nadars.

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