Bayinnaung, the expansionist king of the Toungoo dynasty of Lower Burma, has unified his country and conquered the Shan States.

Taking as a pretext for war the refusal in 1563 of the Siamese to acknowledge his suzerainty, he marches eastward into Siam to overrun and occupy the Thai state of Chiang Mai in 1564.

Bayinnaung’s troops, having overrun the Sukhothai area, seize the Siamese capital city of Ayutthaya in 1564.

King Mahachakrabarti, his Thai subjects opposing war, negotiates a peace and surrenders resistance leaders, including a son, to the invaders.

Under the treaty, Mahachakrabarti’s son Mahindra assumes control of Siam.

Bayinnaung brings the Siamese royal family as hostages to Pegu, his capital, burned in a Mon revolt in 1564.

He rebuilds Pegu on an even grander scale, making it one of the richest cities in Southeast Asia.

A patron of Buddhism, Bayinnaung builds pagodas, gives generous donations to monasteries, and maintains extensive diplomatic relations with the Sinhalese Buddhist Kingdom of Kandy on Ceylon.

Setthathirat I, sovereign of the Lao kingdom of Lan Xang, had married a princess from Ayutthaya and formed a political alliance with the Thai against their common enemy, Burma.

Burmese forces now move west from Chiang Mai to invade laotian territory and besiege Vien Chan (now Vientiane), Setthathirat’s new capital, but withdraw from the area in 1565 the face of fierce and continuous Laotian resistance.