Sukhothai and Lanna
Thai city-states gradually became independent from the weakened Khmer Empire. It is said that Sukhothai was established as a sovereign, strong kingdom by Pho Khun Si Indrathit in 1238 AD. A political feature which "classic" Thai historians call "father governs children" existed at this time. Everybody could bring their problems to the king directly, as there was a bell in front of the palace for this purpose. The city briefly dominated the area under King Ramkhamhaeng, who established the Thai alphabet, but after his death in 1365, Sukothai fell into decline and became subject to another emerging Thai state: the Ayutthaya Kingdom in the lower Chao Phraya area.
Another Thai state that coexisted with Sukhothai was the eastern state of Lanna, centred in Chiang Mai. King Phya Mangrai was its founder. This city-state emerged in the same period as Sukhothai. Evidently Lanna became closely allied with Sukhothai. After the Ayutthaya kingdom had emerged and expanded its influence from the Chao Phraya valley, Sukhothai was finally subdued. Fierce battles between Lanna and Ayutthaya also constantly took place and Chiang Mai was eventually subjugated, becoming Ayutthaya's 'vassal'.
Lanna's independent history ended in 1558, when it finally fell to the Burmese; thereafter it was dominated by Burma until the late 18th century. Local leaders then rose up against the Burmese with the help of the rising Thai kingdom of Thonburi of king Taksin. The 'Northern City-States' then became vassals of the lower Thai kingdoms of Thonburi and Bangkok. In the early 20th century they were annexed and became part of modern Siam, the country now called Thailand.
Read more about this topic: Siam