Naga Kingdom
In the Mahabharata the Naga Kingdom is the territory of a hardy and warlike tribe called Nagas. They were also considered as one of the supernatural races like the Kinnaras.
The Sanskrit word Naga
The word Naga in the Sanskrit language means snake or serpent.
It seems likely that the Naga people were a serpent-worshipping group who were later described as serpents
themselves in ancient Indian literature. Ayus people were Serpent cult people from the beginning.
Serpents are reptiles with "hoods". Snakes are reptiles without hoods.
Maha Vishnu's Shesha NAAG was a huge serpent with 5 hoods. That needs to be differentiated from Shiva's one headed snake.
References in Mahabharata
Mahabharata epic begins with history of Nagas, in astonishing detail, spanning the initial chapters in the first book (Adi Parva). These chapters were distributed into three sub-volumes called Paushya, Pauloma and Astika.
Naga races
MBh (1,57)
Naga race in north-west India was almost exterminated by Janamejaya, the Kuru king in Arjuna's line, who conducted the massacre of Nagas at Takshasila. This massacre was stopped by Astika, a Brahmin whose mother was a Naga. The names of the principal Nagas known widely for their achievements, and slain by Janamejaya is mentioned at (1,57). They were described to be belonging to different Naga races:-