Buddha during the time of his passing (~400BCE) said,
“Ananda, so long as the Vajjians hold these full and frequent public assemblies, meet together in concord and carry out their undertakings…and act in accordance with their ancient institutions…so long as they honour and esteem, revere and support the Vajjian elders…and hold it a point of duty to hearken their words…so long may the Vajjians be expected not to decline but to prosper.”
– Mahanibbana Sutta, Buddhist canonical text
Buddha was referring to the republican government of the Licchavi clan of the Vajji state. One of the chief 16 states existing since 600 BCE in the subcontinent. He was so impressed by the house of of 7,707 representatives which discussed all important questions, by its conduct of proceedings and management of the Vajjian and other republican state affairs that Buddha adopted this democratic constitution for the Buddhist Sangha.
This is just and example of the multiple states which were republican in nature during 600 BCE in South Asia. The operation and management of the political theory of these states have been well recorded by the Greek and the Chinese historians and the indigenous scholars. Most of the states which repelled Alexander’s inavasion were in fact republican in nature.
Panini the grammarian, in his work Ashtadhyayi (~600BCE) recounts that atleast 14 states had republican governments. Firmly placing the history of South Asian republican governments 200 years earlier than Greek republican governments.
Very interestingly the author of Shanti parva (Chp 107) from the great epic Mahabharata states a fact about democratic republics that has remained relevant through these millennia. He proposes that democratic republics face two main dangers of disunion and dissension. To counter these the principal members of these states should have forbearance and tolerance. It is the internal dangers fomented by the enemies by creating disunion and corruption, that a democratic republic should guard against. The external danger is is not of much importance.