Vatsa or Vamsa (Pali and Ardhamagadhi: Vaccha, literally "calf"[1]) was one of the sixteen Mahajanapadas (great kingdoms) of Uttarapatha of ancient India mentioned in the Aṅguttara Nikāya.

During the Rig Vedic period, the Kuru Kingdom comprised the area of present day Haryana/ Delhi and the Ganga-Jamuna Doab, till Prayag/ Kaushambi, with its capital at Hastinapura.

In the post Vedic period, when Aryavarta consisted of several Mahajanapadas, the Kuru Dynasty was split between Kurus and Vatsas.

The Puranas state that after the washing away of Hastinapura by the Ganges, the Bhārata king Nicakṣu, the great-great grandson of Janamejaya, abandoned the city and settled in Kauśāmbī.

According to the Jain canonical texts, Udayana was still a minor when Śatānīka died, so "the responsibility of governing the kingdom fell on the shoulders of queen Migāvatī ... till her son grew old enough".

[7] On the other hand, Bhāsa's Pratijñāyaugandharāyaṇa says that she took "full charge of the administration" while Udayana was held as a prisoner by King Pradyota of Avanti, and "the way in which she discharged her duties excited the admiration of even experienced ministers".