The Forty Years' War (1385 – 1424; also Ava-Pegu War or the Mon-Burmese War) is a military conflict fought between the Burmese-speaking Kingdom of Ava and the Mon-speaking Kingdom of Hanthawaddy Pegu.
The war is fought during two separate periods: 1385 to 1391 and 1404 to 1424, interrupted by two truces of 1391–1404 and 1406–1407.
It s fought primarily in today's Lower Burma and also in Upper Burma, Shan State and Rakhine State.
It ends in a stalemate, preserving the independence of Hanthawaddy, and effectively ending Ava's efforts to rebuild the erstwhile Pagan Empire.
