Small passage to whet your interest:
>It is also essential to mix all the nationalities together in divisions, regiments and battalions. If one regiment contains too many Lithuanians and another too many Tatars, this must result from a slip-up by some military bureaucrat. The punishment for such mistakes is harsh. The movement of such colossal numbers of men takes up two whole months. Surprisingly, the machine works extremely smoothly, rather like a sausage machine-all sorts of pieces of meat, some onions, some rusks, and some garlic are put in at one end and out of the other come solidly compressed rolls of well-mixed human material.
The author is an excellent writer and the rest of this book is worth a read. Some facts are a little iffy, but I believe that's mostly it was published prior to the Soviet Union opening up its archives/making primary sources readily available.