Siouan languages
In the 19th century, Robert Latham suggested that the Siouan languages are related to the Caddoan and Iroquoian languages. In 1931, Louis Allen presented the first list of systematic correspondences between a set of 25 lexical items in Siouan and Iroquoian. In the 1960s and 1970s, Wallace Chafe further explored the link between Siouan and Caddoan languages. In the 1990s, Marianne Mithun compared the morphology and syntax of all the three families. At present, this Macro-Siouan hypothesis is not considered proved, and the similarities between the three families may instead be due to their protolanguages having been part of a sprachbund.
Isan language
Isan speakers became politically separated from other Lao speakers after the Franco-Siamese War of 1893 would lead Siam to cede all of the territories east of the Mekong to France, which subsequently established the French Protectorate of Laos. In 1904, Sainyabuli and Champasak Provinces were ceded to France, leading to the current borders between Thailand and Laos. A 25 km demilitarised zone west of the river banks allowed for easy crossings, and Isan remained largely neglected for some time. Rebellions against Siamese and French incursions into the region included the Holy Man's Rebellion (1901-1904), led by self-proclaimed holy men. The Lao people also joined in the rebellion, but was crushed by Thai troops in Isan. At first, Isan was administered by Lao local rulers subject to the Siamese Court under the monthon system of administration, but this was abolished in 1933, bringing Isan under the direct control of Bangkok.