If Intharathit King founded the kingdom of Sukhothai in 1238 and extend his dominion over the Khmer Empire and remote areas of southern Thailand today , while under the influence of Sirivijaya .
The latter, whose capital was on the Indonesian island of Sumatra controlled the main trade routes between China and India for centuries. Bang Klang Tao who succeeded his father and reigned under the name of Rama Kamhèng the Great.
He continues the conquest of the kingdom of Sukhothai and seized the Malay Peninsula to the location of the current Singapore, always at the expense of Sirivijaya empire. According to legend, the sovereign modify the Sri Lankan writing to create the Thai alphabet .
Thailand becomes the hub of trade ( cotton canvas , silver and copper , silk , porcelain and tea , tin, pepper, spices, aromatic woods , resins, rhinoceros horns , pearls, birds' nests , and deer skins sugar) between China , Japan , India and the Arabian Peninsula.