King U-Thong and his immediate successors expanded Ayutthaya's territory, especially northward towards Sukhothai and eastward towards the Khmer capital of Angkor. The greater size of government could not remain the same as during the days of King Ramkhamhaeng. The society during the Ayutthaya period was strictly hierarchical. There were, roughly, three classes of people king at the top of scale. At the bottom of social scale were commoners and the slaves.
In the early 16th century, the European visited Ayutthaya, and a Portuguese embassy was established in 1511. Portugal's powerful neighbor Spain was the next European nation to arrive in Ayutthaya forward the end of the 16th century. In he early 17th century they saw the arrival of two northern European, the Dutch and the British, and France in 1662.
In the mid-16th century, Ayutthaya and the independent kingdom in Chiang Mai was put under the control of the Burmese, but Thais could regain both of the capitals by the end of the century.
The Burmese invaded Ayutthaya again in 1765. This time Burmese caused much fear to Thais. Burmase soldiers destroyed everything, including temples, manuscripts, and religious sculpture. After the capital fell in their hands for two years, the Burmese effectiveness could not further hold the kingdom. Phaya Taksin, a Thai general, promoted himself to be the king in 1769. He ruled the new capital of Thonburi on the bank of Chao Phraya River, opposite Bangkok. Thais regained control of their country and thus scattered themselves to the provinces in the north and central part of Thailand. Taksin eventually turn himself to be the next Buddha and was dismissed and executed by his ministers who did not approve his religious values.