thumb|240px|Map showing geographic distribution of Kra–Dai linguistic family. Arrows represent general pattern of the migration of Tai-speaking tribes along the rivers and over the lower passes. thumb|240px|Lan Na kingdom during the reign of Tilokaraj ( 1441–1487) Theoretically, Tai-Kadai-speaking people formed as early as the 12th century BCE in the middle of the Yangtze basin. Some groups later migrated south to Guangxi. However, after several bloody centuries against Chinese influence in Guangxi between 333 BCE and the 11th century, hundreds of thousands of Tais were killed, thus, Tai people began to move southwestward along the rivers and over the lower passes into the mountain north of Southeast Asia and river valleys in present-day Assam of India. Some evidence indicates that the ancestors of Tai people migrated en masse southwestwards out of Yunnan only after the 1253 Mongol invasion of Dali; however, it is not generally accepted.
thumb|240px|Map showing geographic distribution of Kra–.Dai linguistic family. Arrows represent general pattern of the migration of Tai-speaking tribes along the rivers and over the lower passes. thumb|240px|Lan Na kingdom during the reign of Tilokaraj ( 1441–1487) Theoretically, Tai-Kadai-speaking people formed as early as the 12th century BCE in the middle of the Yangtze basin. Some groups later migrated south to Guangxi. However, after several bloody centuries against Chinese influence in Guangxi between 333 BCE and the 11th century, hundreds of thousands of Tais were killed, thus, Tai people began to move southwestward along the rivers and over the lower passes into the mountain north of Southeast ,Asia and river valleys in present-day Assam of India. Some evidence indicates that the ancestors of Tai people migrated en masse southwestwards out of Yunnan only after the 1253 Mongol invasion of Dali; however it is not generally accepted