Look up Panini on google, etc. He was a famous grammarian of the Vedic Period. The Greek emissary was Megasthenes, who apprised the west of India's advanced methods of irrigation, etc.; the ancient Graeco-Roman historians' data on the civilizations of India almost exclusively were borne out of his accounts, c. the last decade of the 300s BCE. The Pali Canon and its sub-categories is a collection of scriptures
Moreover, the ancient 'republics' of India require much extrapolation, but for all in all, they seemed to have been organized before the Greek city-states began their experiments with non-monarchical body-politics. The Licchavi tribe may have formed the first 'democracy', in a very broad sense (not completely by modern conceptions, either), out of their capital of Vaisali. A modern historian who passed away recently was one Jagdish Sharma: anything by him will be very elucidating. I don't know if he's related to an earlier eminent historian on ancient India, one Ram Sharma. The Arthashastra is an ancient treatise concerned with war practice, and was perhaps authored, at least partly, by a contemporary of Megasthenes - Kautilya (Chanakya), who was the 'right-hand' man to the great Chandragupta Maurya. The historic accounts are a big part of two famous ancient Indian epics (like the Iliad or Aeneid) - the Mahabharata and Ramayana.
Hope this helped :)