Starting in the middle of the 16th century, the kingdom came under repeated attacks by the Taungoo Dynasty of Burma. The Burmese–Siamese War (1547–49) began with Burmese an invasion and a failed siege of Ayutthaya. A second siege (1563–64) led by King Bayinnaung forced King Maha Chakkraphat to surrender in 1564. The royal family was taken to Bago, Burma, with the king's second son Mahinthrathirat installed as the vassal king.[8][9] In 1568, Mahinthrathirat revolted when his father managed to return from Bago as a Buddhist monk. The ensuing third siege captured Ayutthaya in 1569 and Bayinnaung made Mahathammarachathirat his vassal king.[9]
King Naresuan enters an abandoned Bago, Burma in 1600, mural painting by Phraya Anusatchitrakon, Wat Suwandararam, Ayutthaya Historical Park.
After Bayinnaung's death in 1581, uparaja Naresuan proclaimed Ayutthaya's independence in 1584. The Thai fought off repeated Burmese invasions (1584–1593), capped by an elephant duel between King Naresuan and Burmese heir-apparent Mingyi Swa in 1593 during the fourth siege of Ayutthaya in which Naresuan famously slew Mingyi Swa (observed 18 January as Royal Thai Armed Forces day). The Burmese–Siamese War (1594–1605) was a Thai attack on Burma, resulting in the capture of the Tanintharyi Region as far as Mottama in 1595 and Lan Na in 1602. Naresuan even invaded mainland Burma as far as Taungoo in 1600, but was driven back.
After Naresuan's death in 1605, northern Tanintharyi and Lan Na returned to Burmese control in 1614.[10]
The Ayutthaya Kingdom's attempt to take over Lan Na and northern Tanintharyi in 1662–1664 failed.[11]