The early Thais migrated south from China, populating the fertile valleys south of the Mekong. The Sukhothai period (1238-1438), Thailand's first dynasty, is considered the golden age of Thai culture. The Thais befriended and traded with neighbouring countries, absorbing elements of various civilizations. The Thai kings of the Ayutthaya Period (1351-1767) expanded Siam's territory, especially eastward towards the Khmer capital of Angkor, but were defeated by the Burmese. After an interlude in Thonburi, the capital was moved to Bangkok in 1782. King Rama III (1824-1851) developed relations with western nations, while King Rama IV (1851-1868) of "The King and I" fame concluded treaties with European countries, avoided colonization, and established modern Thailand. The Constitution of 1932 ended 700 years of absolute monarchy.