Thailand
Mon and Lavo Kingdoms: (5th century CE – 13th century CE)

As is generally known, the present-day Thai people were previously called Siamese before the country was renamed Thailand in the mid-20th century. Several genetic studies published in the 21st century suggest that the so-called Siamese people (central Thai) might have had Mon origins since their genetic profiles are more closely related to the Mon people in Myanmar than the Tais in southern China, and they probably later became Tais via cultural diffusion after the arriving of Tai people from the north around the 8th–10th centuries. This is also reflected in the language since over half of the vocabulary in the central Thai language is derived from or borrowed from the Mon language as well as Pali and Sanskrit. Moreover, the Jinakalamali chronicle of Tai's Lan Na also called the southern region occupied by the Mon Haripuñjaya of Dvaravati as Shyam Pradesh (lit. ' the land of Siam people '), which indicates that the ancient Siamese and the Mon people in central Thailand were probably the same ethnolinguistic group.

The earliest evidence to mention the Siam people are stone inscriptions found in Angkor Borei of Funan (K.557 and K.600), dated 661 CE, the slave's name is mentioned as "Ku Sayam" meaning "Sayam female slaves" (Ku is a prefix used to refer to female slaves in the pre-Angkorian era), and the Takéo inscriptions (K.79) written in 682 during the reign of Bhavavarman II of Chenla also mention Siam Nobel: Sāraṇnoya Poña Sayam, which was transcribed into English as: the rice field that was given to the poña (noble rank) who was called Sayam (Siam). The Song Huiyao Jigao (960–1279) indicate Siamese people settled in the west central Thailand and their state was called Xiān guó (Chinese: 暹國), while the eastern plain belonged to the Mon of Lavo (Chinese: 羅渦國), who later fell under the Chenla and Khmer hegemony around the 7th–9th centuries. Those Mon political entities, which also included Haripuñjaya in the north and several city-states in the northeast, are collectively called Dvaravati. However, the states of Siamese Mon and Lavo were later merged via the royal intermarriage and became Ayutthaya Kingdom in the mid-14th century, while the southwestern Isan principalities, centered in Phanom Rung and Phimai, later pledged allegiance to Siamese's Ayutthaya during the reign of Borommarachathirat II (r. 1424–1448). The remaining principal city-states in Isan region became Lan Xang around 1353 after the twin cities of Muang Sua (Luang Prabang) and Vieng Chan Vieng Kham (Vientiane) became independent following the death of the Sukhothai king Ram Khamhaeng.

According to the Wat Kud Tae inscription (K.1105), dated c. 7th century, during the period that the eastern Mon entity, Lavo, was strongly influenced by the Chenla, the Siamese Mon in the west also established a royal intermarriage with Chenla as Sri Chakatham, prince of Sambhuka (ศามภูกะ, in the present-day Ratchaburi province), married to a princess of Isanavarman I, and two mandalas then became an ally. After Chenla sieged Funan and moved the center to Angkor, both Siamese Mon and the Angkorian eventually marched the troops to attack Vijaya of Champa in 1201 during the reign of Jayavarman VII, as recorded in the Cho-Dinh inscription (C.3).
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