Firstly, there are major trigger warning, especially for Under the Yoke. There is one particularly bad rape scene. Do not read the books if you want a happy, light or fun read.
These books take place in a world where the Loyalists from the American Revolution and the Confederates from the Civil War create a hellish society in South Africa. In the aftermath to World War II it becomes the major power in lieu of the Soviet Union. This society is called the Domination of the Draka.
Marching Through Georgia is from the perspective of a liberal Draka who cannot act outside his culture. It asks the reader what s/he would do if they were a Draka. It only holds together because almost no one likes the Nazis and Stirling is a good writer. The second book is from the perspective of newly caught serfs. It emphasises that no matter what you do as a serf, in the hands of a ruthless and intelligent ruling class you cannot win. The most you can hope for is survival. As a consequence the book is stomach-twistingly awful if you have even a shred of empathy.
It dispels any comforting notions people might have about slavery.
Very heavy content. Two stars.