The scholarship I'm familiar with emphasizes Nazi borrowing from American race laws more broadly (anti-miscegenation laws and citizenship restrictions). The book to read is Whitman, Hitler's American Model.

Also important to note that the Nazis are not the first German perpetrators of genocide - see the genocide of the Herero in what is now Nambia.

The genesis of the idea of the concentration camp itself (distinct from its use as part of a genocidal project) is generally traced to the South African War (ie, the Anglo-Boer War). A recent history of the roots of the British concentration camp is Forth, Barbed Wire Imperialism.