1538–39: 1541–42: 1543–44: 1544–45: 1538–1539: 1541–42: 1543–44: 1544–45: The Toungoo–Ava War (1538–1545) (Burmese: တောင်ငူ–အင်းဝ စစ် (၁၅၃၈–၁၅၄၅)) was a military conflict that took place in present-day Lower and Central Burma (Myanmar) between the Toungoo Dynasty, and the Ava-led Confederation of Shan States, Hanthawaddy Pegu, and Arakan (Mrauk-U).

After its troops broke the siege of Prome in 1539, Ava got its Confederation allies agreed to prepare for war, and formed an alliance with Arakan.

[10] But the loose alliance crucially failed to open a second front during the seven dry-season months of 1540–41 when Toungoo was struggling to conquer Martaban (Mottama).

Due to poor coordination, the armies of the Ava-led Confederation and Arakan were driven back by better organized Toungoo forces in April 1542, after which the Arakanese navy, which had already taken two key Irrawaddy delta ports, retreated.

Another former vassal state Toungoo (Taungoo), hemmed in by the Bago Yoma range in the west and the Shan Hills in the east, stayed out of the internecine warfare raging in Upper Burma.

"[17] Fortunately for Toungoo, Sawlon I was assassinated in 1533 on his return trip from Prome, and his son and successor Thohanbwa, based out of Ava, was not accepted as the first among equals by other saophas (chiefs) of the Confederation.

[19] Although a united polity of Toungoo and Pegu could in theory challenge their possessions in western central Burma (the Prome to Pagan corridor along the Irrawaddy), the Confederation's fractured leadership took no action.

[20] Closer to the battleground, however, King Narapati of Prome was increasingly concerned by Toungoo's deeper and longer raids with each successive campaign, and raised the alarm with Ava.

[24] While a flatfooted Thohanbwa scrambled to round up the troops, about 7000 Toungoo land and naval forces[note 1] converged on Prome, the gateway to central Burma.

Finally, 5000 Ava troops arrived in 300 war boats to break up the siege, and chased Toungoo forces back to the delta.

In order to consolidate his gains in Lower Burma, Tabinshwehti moved his capital to Pegu in 1539; reappointed former Hanthawaddy lords to their posts; and appointed many of them to the highest positions of his government.

This fortuitous combination of Toungoo's "more martial culture", and Lower Burma's manpower, access to foreign firearms, and maritime wealth to pay for them would enable the men from a "small frontier outpost" to further wage war on their neighbors in the following decades.

[10] At Martaban, the only remaining independent Hanthawaddy province, its ruler Saw Binnya had completely fortified his wealthy port, and enlisted Portuguese mercenaries and warships in his service.

[31] Although the siege presented the Confederation and Arakan with several opportunities to attack Toungoo's lightly defended northern perimeter and southern delta,[note 2] they took no action.

By the start of the next dry season in November 1541, neither Ava nor Mrauk-U had raised any sizable standing armies that could be dispatched to Prome.

In case of a long siege, they would take positions around the city would prevent Ava and Arakan forces from linking up, and they would drive the enemy separately.

Their armies were to break the siege while the well-regarded Arakanese navy, equipped with Portuguese weaponry and mercenaries, was to invade the delta from the south.

It was only in April 1542 that the Confederation armies (16,000 troops, 1,000 horses, 80 elephants), led by Thohanbwa and Hkonmaing I of Onbaung–Hsipaw, the chief of Onbaung, approached the northern perimeter.

[40] Though both sides suffered heavy casualties, it proved to be a strategically important victory for Toungoo since it took the Confederation out of the equation for the time being.

Right after the battle, the Toungoo command received intelligence that the Arakanese army led by Min Aung Hla, Viceroy of Sandoway (Thandwe),[note 4] was crossing the Arakan Yoma range at the Padaung Pass, and that a sizable Arakanese navy led by Crown Prince Min Dikkha[note 5] was sailing past Cape Negrais.

But others including Bayinnaung disliked an outright lifting of the siege because Prome's forces, they feared, could join in on an attack from the north.

But Tabinshwehti made it clear through his emissaries that he no longer had to worry about Ava or Arakan, and that he would continue the siege even during the rainy season.

[47] In the end, in August/September 1542,[note 8] the chiefs reluctantly decided to back Hkonmaing, and form a united front against a rising Toungoo.

The chiefs apparently were not able to persuade King Min Bin of Arakan to stay in the alliance; Mrauk-U did not contribute any troops.

[51] They moved most of their troops from the Toungoo theater, and massed all their land and naval forces at Tharrawaddy (Thayawadi), about 160 km south of Prome.

They hastily planned to make a stand at Salin long enough for them to prepare their defenses farther (90 km) north in Pagan (Bagan).

When the dry season of 1544 arrived, they saw no Toungoo armies on the horizon, and ultimately decided on a limited attack across the new ill-defined border.

[13] In April/May 1545, Sawlon II sent Sithu Kyawhtin with an army (5000 men, 800 horses, 60 elephants), which went on to occupy Sagaing, the city directly across the Irrawaddy from Ava.

The new king promptly sent a mission to Pegu to secure friendly relations in exchange for his recognition of the new de facto border between the two kingdoms.

[57] In the following years, Ava and Mohnyin-backed Sagaing would be locked in a war until 1551,[58] while an emboldened Toungoo would turn its attention to conquering Arakan in 1545–47, and Siam in 1547–49.