"Bloodlands: Europe Between Hitler and Stalin" by Timothy Snyder, is a book about the intentional mass murder of over 14 million people between 1930 and 1947 in a general area that encompasses what is now Poland, Latvia, Lithuania, Estonia, Belarus, Ukraine, and western Russia. And by murder, I mean that. As part of that 14 million number, Mr. Snyder counts only those that were outright killed, intentionally starved, or otherwise were put to death outside of military actions or by being worked to death. If you were to include the deaths that could have been predictably forseen as a result of certain actions taken, that number jumps to between 17 and 21 million people who were killed.
The author breaks the killing periods into 5 general subsets ... Stalin starving the Ukrainian kulaks in 1932-1933, Stalin's Great Terror of 1937-1938, Hitler and Stalin murdering and otherwise removing Polish, Latvian, Lithuanian, and Estonian intelligentsias from 1939-1941, Hitler's murdering the Jewish population and "undesirables" of many countries, intentionally starving Russian POWs and Soviet civilians, and executing civilians as part of partisan reprisals in 1941 - 1945, and people who died as a result of forced resettlements in 1945-1947.
While I've read extensively about World War II, I learned a great deal from this book. As one example, there were no purely death camps in Germany proper, the Germans built those in occupied Poland. While there were concentrations camps in Germany and many of these camps contained extermination chambers, their primary function was as forced-labor camps. Personnel assigned to the labor camps had a slim chance of surviving. There were 6 death, or extermination, camps set up in Poland ... Auschwitz, Chelmno, Belzed, Majdanek, Soribor, and Treblinka. Only Auschwitz and Majdanek had labor camps attached to them, the other 4 existed purely to murder people. Of the people who arrived at the death camps other than Auschwitz (and for a time, Jewish prisoners at Majdanek), they were all usually killed within hours of arrival, and of those sent there, only about 100 people saw the inside of the camp and lived to tell of it. At Auschwitz, new arrivals were separated into those who would be killed immediately, and those who would work in the labor camp until they weakened and then they were killed. The survivor's tales from Auschwitz come from those assigned to the labor camps.
This book attempts, with great success, to show the vast scope of death in the bloodlands, and how Hitler's and Stalin's extermination policies were alike and how they differed. He also shows how the Wehrmacht was much more complicit in atrocities than the German soldiers of the time would have liked you to believe, and how international and allied policies overlooked much of the killing for a variety of reasons.
The book is grim reading, and while it is more of a scholarly study of the depredations of Hitler and Stalin, there are anecdotes contained within that are heartbreaking, such as the Polish-Jewish mother breastfeeding her infant mere seconds before they're shot, and a starving Ukrainian toddler hallucinating that he sees the food that will save his family's lives. It is not a sensationalist text; it calmly, objectively, and concisely discusses the horrors that occurred.
I highly recommend this book. It is the first book I've read that ties so many of the atrocities committed against the helpless into one highly readable and informative tome, and shows them as part of a larger tapestry against the framework of the times.