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.
Lumbee
After repeated rejections under the Croatan, Cherokee and Cheraw labels, the proto Lumbee petitioned the United States Bureau of Indian Affairs in 1924 for recognition as "Siouan" Indians. This petition was rejected largely on the grounds that Siouan was a language, not a tribe. Moreover, there was no record of the Lumbee or their ancestors having ever spoken the Siouan or any other Indian language.