The Museum of Tatarstan Statehood History sits inside the Kazan Kremlin in the restored old Cadet Corps building. It covers the Volga Bulgar state, the Khanate of Kazan, Russian rule, and modern Tatar autonomy with a useful linear chronology that fills in the gaps left by the more general National Museum.
The display includes original treaties, royal seals, archaeology from the Bulgar period, and a slightly hagiographic section on the modern Republic. English captioning is patchy. Combine with the rest of the Kremlin in a single visit.