Circassia was basically destroyed by the Russian conquest, most Circassians moving on to live in turkey, some being settled by the ottomans as military colonies in Palestine (where some continue to live to this day). So when they or their military history do show up, it tends to be in histories of Russia or Turkey or Iran.
Or Egypt! Because in the latter part of the Mamluk period, most of them were Circassians.
The best survey in English is probably “The Circassians: A Handbook,” by Amjad Jaimoukha.