It's an excellent book, lives up to the great reviews and prizes. It traces the history of genocide beginning in the early 1900s with the extermination of the Armenians in Turkey. It gives a detailed history of the man who created the term, "genocide" and his crusade to make this a world crime, beyond any borders.
Although he was successful in some respects he did not succeed in getting nations to respond to genocide happening in other parts of the world, particularly within a nation's borders. The typical response of all nations to evidence of genocide has been to call it something else - usually to say the conflict is two-sided, to disbelieve the reports (with some good reason, given the lack of accuracy of reporting in many cases), to rationalize in many different ways that it is "no concern of ours".
The farther away we are from an event the less it means to us. A human response, I'm sure, a way of coping with what we can. I also see, though, our extraordinary lack of memory. We commemorate and discuss and preach about the holocaust endlessly and say "We must remember", "It must never happen again", yet we let it happen again and again. Not at the scale, not yet, but that doesn't mean it won't.
I am good at getting worked up about these things, but I rarely do anything all that concrete about any of it. Some people dedicate their lives to making a real change, and I'm not like that. Perhaps being aware and talking about these things helps, though.