The Magadha–Kosala War was a military conflict between the Haryanka dynasty of Magadha and the neighbouring Kosala kingdom.
The conflict is mentioned in ancient Indian literature of Hindus, Buddhist and Jain traditions.
After the Buddha's death he invaded the Sakya and Koliya republics, seeking to conquer their territories because they had once been part of Kosala.
Viḍūḍabha finally triumphed over the Sakyas and Koliyas and annexed their state after a long war with massive loss of lives on both sides.
[1] The heavy loss of life incurred by Kosala during its conquest of Sakya weakened it significantly enough that it was itself was soon annexed by its eastern neighbour, the Kingdom of Magadha, and Viḍūḍabha was defeated and killed by the Māgadhī King Ajātasattu.