Chao Phraya Basin under the Tai

There are several legends about the Tai coming to rule mandalas of Central Thailand including Lavo and Suphannabhum. The Suphannabhum mandala had been independent of Khmer influence and composed originally of the Western Provinces of modern Thailand including Suphanburi, Ratchaburi, and Phetchaburi. In the 12th century, the Tai Po Khuns of the upper Chao Phraya coalesced around the Po Khun of Sukhothai - an important Khmer outpost. With the weakened Khmer authority, Po Khun Si Nau Namthom
of Sukhothai gained the autonomy of the upper Chao Phraya valley. However, during the reign of Jayavarman VII, the Khmer power was strengthened, and the Tai Po Khuns were subdued and brought under Khmer suzerainty. Suphannabhum was also weakened by Khmer invasions and only the city of Suphanburi itself was left.

Sukhothai and Lanna

Thai city-states gradually became independent from the weaker 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 called by 'classic' Thai historians as '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 he died in 1365 it 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 northern state of Lanna, centered 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.

Hariphunchai

According to the Jamadevivamsa, the city of Hariphunchai (modern Lamphun) was founded by the hermits; Jamadevi, a Lavo princess, was invited to rule the city in around 700 AD. However, the date is considered too early for the foundation of Hariphunchai as Jamadevi brought no Thammachakras to the north. Hariphunchai may be a later (about the 10th century) offshoot of the Lavo kingdom or instead related to the Thaton kingdom.
Hariphunchai was the center of Theravada in the north. The kingdom flourished during the reign of King Attayawong who built the Dhatu of Hariphunchai in 1108. The kingdom had strong relations to another Mon kingdom of Thaton. During the 11th century, Hariphunchai waged lengthy wars with the Tai Ngoenyang kingdom of Chiang Saen. Weakened by Tai invasions, Hariphunchai eventually fell in 1293 to Mangrai the Great, king of Lanna, the successor state of the Ngoenyang kingdom

Si Kottaboon

While the Dvaravatians ruled Chao Phraya, Isan was the place of the Si Kottaboon culture, which belonged to the native Mon-Khmer people. Si Kottaboon is regarded as a stem culture of Dvaravati with Mon scripts and oval-shaped cities. The Thammachakras of Dvaravati became the Semas or Stone Leaves of Si Kottaboon. The culture tolerated the Khmer Chenla expansions around the 7th century. The southeasternmost part of Isan was the heartland of the Chenla kingdom that expanded over the southern Funan around the 7th century

Dvaravati

The Chao Phraya valley in what is now Central Thailand had once been the home of Mon Dvaravati culture, which prevailed from the 7th century to the 10th century. The existence of the civilizations had long been forgotten by the Thai when Samuel Beal discovered the polity among the Chinese writings on Southeast Asia as “Tou-lo-po-ti”. During the early 20th century the archeologists led by George Coedès made grand excavations on what is now Nakorn Pathom and found it to be a center of Dvaravati culture. The constructed name Dvaravati was confirmed by a Sanskrit plate inscription containing the name “Dvaravati”.
Later on, many more Dvaravati sites were discovered throughout the Chao Phraya valley. The two most important sites were Nakorn Pathom and Uthong (in the present Suphanburi Province). The inscriptions of Dvaravati were in Sanskrit and Mon using the script derived from the Pallava script of the Pallava dynasty. The religion of Dvaravati is
thought to be Theravada through contacts with Sri Lanka, with the ruling class also participating in Hindu rites. The Dvaravati art, including the Buddha sculptures and stupas, showed strong similarities to those of the Gupta dynasty. The most prominent production of Dvaravati art are the Thammachakras or the Stone Wheels signifying Buddhist principles. The eastern parts of the Chao Phraya valley were subjected to a more Khmer and Hindu influence as the inscriptions are found in Khmer and Sanskrit.

Dvaravati was not a kingdom but a network of city-states paying tributes to more powerful ones according to the mandala model. Dvaravati culture expanded into Isan as well as southwards as far as the Isthmus of Kra. Dvaravati was a part of ancient international trade as Roman artifacts were also found and Dvaravati tributes to the Tang court are recorded. The culture came to an end around the 10th century when it was replaced by a more unified Lavo-Khmer polity.