Adam Bruno Ulam was a Polish-American historian and political scientist at Harvard University. Ulam was one of the world's foremost authorities on Russia and the Soviet Union, and the author of twenty books and many articles.
This is a dense book. It looks at Soviet Policy from 1916-1967 and has a depth to it that is amazing. I have 2-3 dozen bookmarks of things I need to go back and digest, and I'm happy to do it.