"Toungoo Period"; also known as the Second Myanmar Empire in traditional historiography, or simply the Taungoo Dynasty) was the dominant power in mainland Southeast Asia in the second half of the 16th century.

At its peak, Toungoo "exercised suzerainty from present-day Assam, Manipur to the Cambodian marches and from the borders of Arakan to Yunnan" and was the largest empire and the only great power country in the history of Southeast Asia.

[13] By then, Toungoo, along with Prome (Pyay), had received waves of Burmese-speaking migrants, driven out of Upper Burma by the successive Shan raids in the second half of the 14th century, and both southern vassal states had emerged as new centres of economic activity as well as of Burman (Bamar) culture.

A distant member of the Ava royalty, Sithu Kyawhtin remained loyal to Thihathura's successor Minkhaung II (r. 1480–1501), who was greeted with a wave of rebellions by lords of Yamethin (1480), Salin (1481) and Prome (1482).

Three of the states were succeeded by weak rulers: Taka Yut Pi (r. 1526–39) at Hanthawaddy; Bayin Htwe (r. 1527–32) and Narapati (r. 1532–39) at Prome; and Thohanbwa (r. 1533–42) at Ava (Confederation).

[8] Tabinshwehti and his court decided to take advantage of the lull, and break out of their increasingly narrow realm by attacking Hanthawaddy, the larger and wealthier but disunited kingdom to the south.

The king attempted to forge a "Mon–Burman synthesis" by actively courting the support of ethnic Mons of Lower Burma, many of whom were appointed to the highest positions in his government and armed forces.

The conquests ended at a stroke, over two centuries of Shan raids into Upper Burma, and "extended lowland control much farther than Pagan had dreamed possible:" Pegu now “exercised suzerainty from Manipur to the Cambodian marches and from the borders of Arakan to Yunnan.”[1] Bayinnaung's authority would be vigorously contested in the following decade.

[35] Closer to home, he responded to the Mughals' 1576 annexation of Bengal by claiming the entire swath of lands in present-day northeast India, as far west as the Ganges[36][37] and by sending an invasion force to Abakan in 1580.

Able men all over Lower Burma fled military service to become monks, debt slaves, private retainers, or refugees in nearby kingdoms.

Its "stunning military conquests were not matched by stable administrative controls in the Tai world or outlying areas of the Irrawaddy basin," and the "overheated" empire "disintegrated no less rapidly than it had been constructed".

[25] The Toungoo kings retained the traditional three-province structure of the old Hanthawaddy Kingdom;[41] Bayinnaung later annexed the Siamese Province of Mergui into the core administration for its maritime revenues.

Unlike in later periods, Pegu even at the height of the empire maintained no permanent military garrisons, or representatives in the vassal states to keep an eye on the local ruler in the peacetime.

The key innovation was that he required sons of his vassal rulers to reside in the palace as pages, who served a dual purpose: they were hostages for good conduct of their fathers and they received valuable training in Burmese court life.

[1] But even at its peak, the vaunted Toungoo military had trouble dealing with guerrilla warfare, and faced severe logistic issues in suppressing rebellions in remote hill states.

Conscription was based on the ahmudan (အမှုထမ်း, "crown service") system, which required local chiefs to supply their predetermined quota of men from their jurisdiction on the basis of population in times of war.

[77] The earliest extant record of organisation of the Royal Burmese Army dates only from 1605 but the organizational structure of the earlier First Toungoo era is likely to be similar, if not essentially the same.

[80] One crucial factor in Toungoo's success was the army's early adoption of Portuguese firearms (arquebus matchlocks and cast-metal muzzleloader cannon), and formation of musket and artillery units.

Toungoo artillery corps never acquired massive siege guns of Europe but they "used Portuguese cannon to good effect by mounting them on high mounds or towers, and then shooting down into besieged towns".

The First Toungoo Empire was a multi-ethnic society although the concept of ethnicity was still highly fluid, heavily influenced by language, culture, class, locale, and political power.

Over in the central mainland, several linguistically distinct Tai groups coexisted alongside sizeable numbers of Mons, Khmers, and a host of hill minorities.

In the western mainland, even the so-called major ethnic groups—such as Burmans, Mons, Shans—were themselves divided into rival centres, with distinctive local traditions and in many cases different dialects.

In the Irrawaddy valley, for example, north-to-south migrations "pitted newcomers against established populations and encouraged stereotyping both as an emotional response to an alien presence and as a (perhaps unconscious) strategy of group mobilization.

He presented himself as cakkavatti, or World Ruler, par excellence,[105] and formed personal relationships based on the concepts of thissa (allegiance) and kyezu (obligation).

In the Irrawaddy valley, min males on balance were more likely to study for long periods in monasteries, to be knowledgeable in Pali, even Sanskrit; to wear Indian and Chinese textiles, to be familiar with foreign conventions than their hsin-ye-tha counterparts.

Unlike in later periods, monks continued to staff the modest royal secretariats of the regional courts, and most of the Burmese (and certainly Pali) literature of the era were produced by the aristocrats and the clergy.

[65] An enduring legacy of the First Toungoo Dynasty was the introduction of a more orthodox version of Theravada Buddhism (Mahavihara school of Ceylon) to Upper Burma and the Shan States.

[120] Following in the footsteps of Dhammazedi, he supervised mass ordinations at the Kalyani Thein at Pegu in his orthodox Theravada Buddhism in the name of purifying the religion.

Toungoo came of age in a period when the arrival of European firearms and an increase in Indian Ocean commerce enabled lowland polities to project power into interior states.

According to Myint-U, Bayinnaung is the favourite king of the present-day Burmese generals, who often see themselves "as fighting the same enemies and in the same places... their soldiers slugging their way through the same thick jungle, preparing to torch a town or press-gang villagers.