Thado Dhamma Yaza III (, ; also known as Mingyi Hnaung (, ); 1571–1597) was viceroy of Prome (Pyay) from 1589 to 1595, and self-styled king of Prome from 1595 to 1597. Hnaung was initially a loyal vassal of his father King Nanda until 1594 when he openly clashed with his brother Crown Prince Minye Kyawswa. Hnaung revolted in 1595 during the Siamese siege of Pegu (Bago). His revolt started a string of other revolts by the major vassal states of the Toungoo Empire in the next two years. His attempts to take over territories beyond Prome's traditional vassals in the present-day Magwe Region were unsuccessful. The self-proclaimed king was assassinated by Yan Naing, one of his trusted advisers, on the eve of his planned invasion of Upper Burma in 1597.
Early life
The future Thado Dhamma Yaza III was the youngest child of Crown Prince Nanda and his chief consort Hanthawaddy Mibaya. He was born 1571. His personal name was Mingyi Hnaung.
The prince grew up at the Kanbawzathadi Palace the last years of his grandfather King Bayinnaung. On 10 October 1581, Nanda succeeded Bayinnaung, and inherited the Toungoo Empire, the largest empire in Southeast Asia. Hnaung became the third in line of succession behind his elder brothers Mingyi Swa, the heir-apparent, and Minye Kyawswa. But Nanda did not have the support of his major vassals, who ruled what used to be sovereign kingdoms just a few decades earlier. By Hnaung's teenage years in the mid-1580s, the empire had already faced serious rebellions in Ava (Upper Burma) and Siam.
Viceroy of Prome
Accession
Hnaung's first major assignment was to be king of Lan Xang. In September/October 1588, Pegu's vassal king Maha Ouparat of Lan Xang died. Nanda appointed Hnaung the next king of Lan Xang although he had reservations about sending his teenage son to the remote rebellion-prone kingdom. But in November/December, Thado Dhamma Yaza II, Viceroy of Prome, died, and Nanda changed his mind and appointed Hnaung at Prome, a strategic vassal state (present-day western Bago Region and Magwe Region). On , Hnaung became viceroy with the title of Thado Dhamma Yaza III. His official style was King of Prome.
Early tenure
At Prome, one of his main responsibilities was to contribute manpower to his father's increasingly stretched military. At least in the beginning, the young viceroy apparently did not have much control over his own vassal rulers, a group that included Minye Uzana of Salin and Min Shwe Myat of Taingda, sons of the previous viceroy Thado Dhamma Yaza II. In 1590, he could contribute just a regiment to a 24-regiment (20,000-man) invasion force of Siam.
But he still helped out his father in some other way. He agreed to lead an expedition to suppress a rebellion in the Shan state of Mogaung (modern Kachin State). On , he led a 10,000-man army, largely made up of conscripts from Upper Burma, and left for the front. Under his command was an eleven-year old Natshinnaung, his second cousin and the heir-presumptive of Toungoo (Taungoo). (The two grandsons of Bayinnaung would later become adversaries less than five years later.) The campaign was a success. His forces retook the fortified town in early 1591. Hnaung arrived at Pegu triumphantly in April 1591 but the capital was in no mood to celebrate. The fourth invasion of Siam had gone terribly wrong. The Burmese forces led by Crown Prince Mingyi Swa had been thoroughly routed in northern Siam by the Siamese army led by King Naresuan.
Hnaung was asked to join the debilitating war effort. By then, the tide was turning in favor of the former vassal state. In the dry season of 1591–92, Siam invaded Burma for the first time. Naresuan and his army advanced as far as Martaban (Mottama) before they were driven back. The Tenasserim coast now fell under Siamese control. The Pegu court responded by planning yet another invasion of Siam. Mingyi Swa would again lead the invasion with Hnaung and Natshinnaung as deputies. On , three armies with a combined force of 24,000 men, 2000 horses, 150 elephants, left Pegu. The invasion came to a sudden halt on when Mingyi Swa fell in action near Suphan Buri. Hnaung took over as the overall commander-in-chief, and decided to retreat.