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.
Sikaiana language
The people of Sikaiana speak the Sikaiana language or Central Solomon Pidgin English. After WWII, many people from Sikaiana migrated to Honiara, the capital of the Solomon Islands in search of jobs and education (Donner, 2002). This means that there was a decrease in the use of the language, since Sikaiana was not the language mainly used in that area. A decrease in the advantages of using the Sikaiana language increases the endangerment of it.