Myinsaing successfully fended off the second Mongol invasion in 1300–1301, and went on to unify central Burma from Tagaung in the north to Prome (Pyay) in the south.

Between one and two-thirds of Upper Burma's cultivatable land had been donated to religion, and the crown had lost resources needed to retain the loyalty of courtiers and military servicemen.

[3] In the next two years, while the king negotiated a ceasefire and eventually a surrender with the Mongols, the defence of central Burma passed to the army led by three brothers named Athinkhaya, Yazathingyan and Thihathu from Myinsaing.

The Mongols invaded central Burma to reinstate their vassal state but were driven back by the brothers' small but disciplined army.

To win their loyalty, the king appointed Athinkhaya, Yazathingyan and Thihathu viceroys of Myinsaing, Mekkhaya and Pinle, respectively.

According to an inscription dated 19 February 1293, the brothers claimed that they were the ones who defeated the Mongol invaders, and that they were equal to the king of Pagan.

[6] Nonetheless, they agreed to march to Lower Burma when King Wareru of Martaban (Mottama) became a vassal of Sukhothai.

In January 1300, the Burmese army led by Athinkhaya seized lightly manned southernmost Mongol garrisons in Singu and Male, only 70 km from Tagaung.

On 22 June 1300, the emperor declared Kumara Kassapa, a son of Kyawswa, the rightful king of Burma, and ordered an invasion.

In the following dry season, a 12,000-strong Mongol army invaded, and despite taking heavy losses managed to reach Myinsaing on 25 January 1301.

But Myinsaing's defences held, and the Mongols were persuaded to call off the attack on receipt of a considerable bribe on 6 April 1301.

The key vassal rulers were: The political unity the brothers achieved in central Burma was fragile and did not last long in any case.

First, after the evacuation of Mongols in 1303, the brothers were able to bring all three main granaries of the country, Kyuakse, Minbu and Mu, under their rule.

Secondly, they attempted to tackle the problem they inherited from Pagan kings: too much valuable land was donated to religion, and the crown could not collect revenue.

According to the British colonial era scholarship, this was the Age of the Three Shan Brothers (ရှမ်းညီနောင်သုံးဦးခေတ်), modifying the term used in the chronicles (မင်းညီနောင်သုံးဦးခေတ်, lit.

[28] Phayre deemed Theinkha Bo, the father of the brothers, an ethnic Shan since the chronicles say he was a son of sawbwa of Binnaka.

But the historian Michael Aung-Thwin has rejected the assertion, given that no historical evidence of any kind exists to support the claim.