Mongkut (Rama IV) was the first monarch to adopt the title when the name Siam was first used in an international treaty.

[4] In the years after, Northern Thai groups established mueang that evolved into larger states, such as Ngoenyang.

[5][6] However, it was not until the decline of the Khmer Empire in the 13th century that a Central Thai kingdom politically and culturally related to modern Thailand was first founded.

The Phra Ruang dynasty was the only royal lineage that ruled over the Sukhothai Kingdom, the first Central Thai state.

Established by Si Inthrathit in 1238, who declared independence from the Khmer Empire, the dynasty laid the foundations for Thai society.

[7] Under Ram Khamhaeng the Great, the initial Thai script was invented and Therāvada Buddhism was established as the state religion.

[8]: 197 [9]: 25 The dynasty is named after the Traiphum Phra Ruang, a Buddhist cosmology book written by Maha Thammaracha I.