The Hanthawaddy Kingdom (Burmese: ဟံသာဝတီ နေပြည်တော်; Mon: ဟံသာဝတဳ, [hɔŋsawətɔe]; also Hanthawaddy Pegu or simply Pegu) was the dominant kingdom that ruled lower Burma (Myanmar) from 1287 to 1539 and from 1550 to 1552. The Mon-speaking kingdom was founded as Ramaññadesa (Burmese: ရာမညဒေသ, Mon: ရးမည) by King Wareru following the collapse of the Pagan Kingdom in 1287 as a nominal vassal state of the Sukhothai Kingdom and of the Mongol Yuan dynasty. The kingdom became formally independent of Sukhothai in 1330 but remained a loose federation of three major regional power centres: the Irrawaddy Delta, Bago, and Mottama. Its kings had little or no authority over the vassals. Mottama was in open rebellion from 1363 to 1388.

The energetic reign of King Razadarit (r. 1384–1421) cemented the kingdom's existence. Razadarit firmly unified the three Mon-speaking regions together, and successfully fended off the northern Burmese-speaking Ava Kingdom in the Forty Years' War (1385–1424), making the western kingdom of Rakhine a tributary from 1413 to 1421 in the process. The war ended in a stalemate but it was a victory for Hanthawaddy as Ava finally gave up its dream of restoring the Pagan Empire. In the years following the war, Pegu occasionally aided Ava's southern vassal states of Prome and Taungoo in their rebellions but carefully avoided getting plunged into a full-scale war.

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