The Toungoo empire's hold on Siam lasted only as long as its strongman did

King Bayinnaung assembled the largest empire in Southeast Asian history, encompassing the Shan States, Lan Na, Lan Xang, Manipur and the Ayutthaya kingdom. Ayutthaya fell to his armies in August 1569, and Siam became a tributary: an annual tribute of thirty elephants and three hundred catties of silver, with the Burmese granted the right to collect the customs of the port of Mergui. Prince Naresuan was even taken to Burma as a hostage for his father's fidelity.

That hold rested on one man. Bayinnaung died in 1581, aged sixty-six, after a reign of thirty-one years. The empire, as the historian Wood put it, 'whose heterogeneous elements had only been held together by the strong personality' of its founder, passed to his son Nandabayin — 'a man who possessed all his father's ruthlessness and cruelty, but none of his will-power or military capacity.'

The vassal noticed the hollow centre first. Nandabayin ordered two nobles to murder Naresuan on the march, but the would-be assassins, 'touched by his youth and his gallant bearing,' divulged the plot instead. Naresuan declared Siam independent in 1584. The reversal was sealed in the invasion that crossed the frontier in December 1592, when Naresuan met the Burmese crown prince in the celebrated elephant duel; the Burmese prince 'received a wound in the shoulder and fell dead from his elephant.'

Naresuan then carried the war into Burma. His invasions were, in Wood's verdict, 'the indirect cause of the fall of Nanda Bhureng and the disintegration of the Burmese Empire.' The vassal had become the overlord. The dependency Bayinnaung built — tribute, customs, hostages — had been enforced by one man, and it did not survive him.