Basically, Siouan, Caddoan and Iroquoian (which includes Cherokee) are all closely related to each other and belong to a larger "Hokan-Siouan" Indian language family. "Hokan-Siouan" languages are found mostly in the United States and the St. Lawrence River Valley of Canada. However, a few are found in northwestern Mexico and one, an isolate, all the way down in Colombia.
Algonquian or Algonkian is another family of American Indian languages spoken from Alberta, Canada to North Carolina. It is only distantly related to Siouan and Iroquoian. Some linguists believe that it's nearest relative is the Muskogean family of Indian languages which includes Creek, Choctaw, Chickasaw and Seminole.
All of these language families belong to an older proposed "Proto-Ameridindian" language which was spoken about 12,000 to 15,000 years ago.
So, all told, you have something like:
1)Proto-Amerindian (12,000 years ago) breaks up into > Common-Hokan Siouan (spoken about 3,000 years ago) > Siouan / Caddoan / Iroquoian (formed less than 2,000 years ago).
Plus
2) Proto-Amerindian (12,000 years ago) also breaks up into > Proto-Algonquian-Muskogean (?) (spoken about 3,000 years ago) > Algonquian & Muskogean (formed less than 2,000 years ago).
Joseph Greenberg, Leonard Bloomfield and Edward Sapir are kind of the leading experts on this subject. If you can locate anything they have written, either in books or on the internet by them it will help you futher.
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