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.
Assiniboine language
The Dakotan group of the Siouan family has five main divisions: Dakota (Santee-Sisseton), Dakota (Yankton-Yanktonai), Lakota (Teton), Nakoda (Assiniboine) and Nakoda (Stoney). Along with the closely related Stoney, Assiniboine is an n variety of the Dakotan languages, meaning its autonym is pronounced with an initial n (thus: "Nakʰóta" as opposed to "Dakʰóta" or "Lakʰóta", and "Nakʰóda" or "Nakʰóna" as opposed to "Dakʰód" or "Lakʰól"). The Assiniboine language is also closely related to the Sioux language and to the Stoney language (likewise called Nakoda or Nakota), although they are hardly mutually intelligible.