The mid-fifteenth century saw the slow emergence of new states across mainland and island South-East Asia after a period of substantial political decentralisation and fragmentation, on the one hand, and the withdrawal or ejection of Chinese armies, on the other. The new or reinvigorated states of the region – including Ava (Upper Burma), Pegu (Lower Burma), Ayudhya (today Thailand), and Dai Viet (today Vietnam) – stimulated a new period of martial vigour from the 1450s as they expanded at the expense of their neighbours. In successful campaigns in the 1450s and in 1471, Dai Viet conquered Champa on its southern frontier twice, leaving the Vietnamese state as the permanent hegemon over mainland South-East Asia’s eastern littoral, relegating Champa to a mere tributary shadow of its former self. (See Map 14.) Ava and Pegu waged a bitter war for decades for dominance over the Irrawaddy valley, a contest that spilled over into Arakan, on the Bay of Bengal, mainland South-East Asia’s thin, western littoral. Ayudhya, in the central mainland, made itself the dominant political and military power in the Chao Phraya river valley.