Here is a link to a review of the entire Foundation Trilogy.
Asimov's second collection of Foundation tales takes a bit of a departure from the first. Instead of detailing the ascendancy of the Foundation, its the story of the fall of the Foundation due to graft and corruption, and from an outside influence that Seldon could never have imagined. Its Asimov's attempt to evoke a theme that ran heavy through the rest of his SF literature: That is to say, Entropy. Not only is the Foundation starting to take its new place of power for granted, but the universe conspires against it in a way to bring it to its knees.
Asimov's second "book," Foundation and Empire, tells the story of the elimination of the Empire as a political entity, and the rise of The Mule. One element of style that I have noted in Asimov's writing is that he likes to latch onto one gem technology or idea to develop in his stories, and pretty much ignores all others and uses them however he needs to tell his story. In this series, probably due to its length, he chooses two: atomics and psychohistory. But only psychohistory really takes central stage time and time again. Seldon's science apparently qualifies and quantifies the movements and motivations of the inhabitants of the entire galaxy, and effectively predicts future history. He does it so well infact that he is able to program his hologram to appear in a theater in the center of Terminus City to reappear after each "Seldon Crisis" occurs, so that he can debrief the encyclopedists. Seldon Crises are events in time where Foundation hegemony is challenged. The master plan sets the Foundation up so that they will have what they need far in advance of each Crisis to weather it. The appearances are to reinforce the direction that the Foundation finds itself headed after each Crisis is over. For the first three hundred years Seldon manages to be exact. But the failing of the Seldon Plan is that it cannot take into account aberrations that are not predictable from historical knowledge. Eventually a mutant conqueror arises, The Mule, that Seldon could not predict. The Mule has mental powers, and is able to bend the will of anyone towards his own ends. The risk to the Foundation is very real. If the Mule wins he will create a new race that will likely enslave homo sapiens. If he loses, he will likely take the Foundation down with him, which will leave the galaxy in the position it would have been in had the Foundation not been established in the first place. The Foundation, at the time of the ascendancy of The Mule is headed towards civil war born of the consolidation of power in a new Emperor, and the destruction of the democracy Seldon set up. As the Foundation prepares for the war with its own provinces, The Mule comes along and conquers everyone in his path. In the end of Book 2 the Foundation is defeated and the Mule becomes the First Citizen of a new league of planets. Ultimately the Foundation is saved by the Second Foundation, which actually was set up in the ruins of Trantor. Instead of encyclopedic knowledge, the Second Foundation's goal is to serve as an equalizer that steps in when the Seldon Plan goes awry.
Some have compared the fall of Paul Muad'dib's empire in Dune with the fall of the Foundation in Foundation and Empire. I really do think that Herbert was influenced by Asimov and realized the literary gold that can be gathered by tearing apart what you spent so much time building up. But Asimov's destruction was not as thorough as Herbert's, and the feeling at the end was not as hopeless. Maybe that means that Herbert was the better writer (I certainly think he was). But the upheaval in this book really was the only good thing about it. Asimov is again, as usual, concerned so much with polite discourse that the hatred that these characters should have felt for each other just does not manage to come through adequately. Imagine the things that the Europeans and Central Asians must have said about Genghis Kahn. Imagine what the Mezo Americans said about the Spanish. None of that was there. It was an all out war for survival of governments, and nobody took any drastic action, or even said anything off color. Another feature of Herbert's writing that I particularly liked was that he tended to stay away from describing battle scenes. That worked in Herbet's books because almost all of the action took place before and after the big battles. Asimov tended also to stay away from description of combat, but he set most of his action contemporaneous with the big battles. In that context, his efforts at describing the reasons that the Foundation fell just...fell flat. Three out of five stars.