The First Toungoo Empire (also known as the First Toungoo Dynasty, the Second Burmese Empire, or simply, the Toungoo Empire) is the dominant power in mainland Southeast Asia in the second half of the sixteenth century.

The empire grows out of the principality of Toungoo, a minor vassal state of Ava until 1510.

The landlocked petty state begins its rise in the 1530s under Tabinshwehti who goes on to found the largest polity in Myanmar since the Pagan Empire by 1550.

His more celebrated successor Bayinnaung then greatly expands the empire, conquering much of mainland Southeast Asia by 1565.

He spends the next decade keeping the empire intact, putting down rebellions in Siam, Lan Xang and the northernmost Shan states.

From 1576 onwards, he declares a large sphere of influence in westerly lands—trans-Manipur states, Arakan and Ceylon.

The empire, held together by patron-client relationships, declines soon after his death in 1581.

His successor Nanda never gains the full support of the vassal rulers, and presidesd over the empire's precipitous collapse in the next eighteen years.The First Toungoo Empire marks the end of the period of petty kingdoms in mainland Southeast Asia.

Although the overextended empire proves ephemeral, the forces that underpin its rise are not.

Its two main successor states—Restored Toungoo Burma and Ayutthaya Siam—go on to dominate western and central mainland Southeast Asia, respectively, down to the mid-eighteenth century.