In the early 16th century, the present-day Myanmar comprised several small kingdoms. The two traditional powers that had dominated the Irrawaddy valley since the 14th century, the Kingdom of Ava  and Hanthawaddy Kingdom, were in serious decline. By the 1530s, the old powers had been or were being eclipsed by upstart powers. In Upper Burma, the Mohnyin-led Confederation of Shan States finally finished off Ava in 1527. On the western coast, the Kingdom of Mrauk U was ascendant at the expense of a weak Bengal, extending its reach into the Ganges Delta in 1533. In the south, the Taungoo-Hanthawaddy War  resulted in a Hanthawaddy victory in 1538-39, and Martaban in 1541, giving the men from the small frontier outpost total control of Lower Burma. Taungoo's meteoric rise raised alarm amongst other powers. In 1539, Ava  and Mrauk U entered into an alliance to defend Ava's vassal state of Prome. But their poorly coordinated forces could not stop better organized Taungoo forces from taking over Prome  in 1542. After his army's crushing defeat at Padaung Pass, King Min Bin of Mrauk U left the alliance. Convinced that Taungoo's guns would eventually point toward his kingdom, Min Bin beefed up the already formidable defenses around his capital. In the following three years, Taungoo completed its takeover of central Burma up to Bagan, which Ava formally ceded in exchange for peace in 1545. King Tabinshwehti had now built the largest polity in Burma since the fall of the Pagan Kingdom in 1287. But as his upcoming campaigns in Arakan  and Thailand  show he was still intent on expanding elsewhere.. Which forces were defeated at Prome in 1542?