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.
Catawba people
Albert Gallatin (1836) classified the Catawba as a separate, distinct group among Siouan tribes. When the linguist Albert Samuel Gatschet visited them in 1881 and obtained a large vocabulary showing numerous correspondences with Siouan, linguists classified them with the Siouan-speaking peoples. Further investigations by Horatio Hale, Gatschet, James Mooney, and James Owen Dorsey proved that several tribes of the same region were also of Siouan stock.