information:classification, structural:reformatting, structural:expansion
Upper Burma (1554–1555)

By late 1554, Bayinnaung had assembled a large invasion force (18,000 men, 900 horses, 80 elephants, 140 war boats), the largest mobilization to date. Precautions were taken on the frontiers to guard against attacks from Lan Na, Siam and Arakan. In November 1554, Toungoo forces launched a two-pronged invasion, one up the Sittaung valley and the other up the Irrawaddy valley. Avan defenses, supported by nine Confederation armies (from Bhamo, Kale, Mogaung, Mohnyin, Momeik, Mone, Nyaungshwe, Theinni and Thibaw-Onbaung), could not stop the advance, and the capital Ava fell to the southern forces on 22 January 1555. King Sithu Kyawhtin was sent to Pegu. Bayinnaung appointed his younger brother Thado Minsaw viceroy of Ava. Toungoo forces then drove out the remaining Confederation armies from the Chindwin valley up to Monywa, the Mu valley up to Myedu and the Kyaukse valley up to Singu by late March.

Bayinnaung now controlled both the Irrawaddy and Sittaung river valleys, the corridors to and from the "heartland" where most of the food of the country was produced and its population lived. Still, his hold on Upper Burma was small—his northernmost outpost Myedu was only about 160 km (100 miles) from Ava—and tenuous since he had not secured the allegiance of the surrounding Shan states, which had been the source of constant raids into the upcountry since the 14th century, and indeed dominated much of it since the early 16th century. He needed to bring the surrounding unruly states under control if his hold on Upper Burma was to last.