The Kasai region of the Democratic Republic of the Congo is divided administratively into Kasai-Occidental and Kasai-Oriental. It shares its name with the Kasai River.
After the independence of Congo, it seceded for a while under influence of Belgium and became an independent kingdom. After the assassination of Patrice Lumumba, Kasai came back to Congo.
References
Kasai region Wikipedia(Text) CC BY-SA