Absolutely terrifying, a must read. Zimbardo is the mad scientist behind the famed Stanford Prison Experiment (SPE) which took place in the 70s. A group of entirely typical and mentally stable college-aged kids were thrust into a mock-prison environment where they were rapidly transformed into sadistic prison guards and downtrodden prisoners. Set up in the basement of a Stanford building used as a mock-prison, participants were randomly assigned to roles: either inmates or guards. In mere days the "guards" became increasingly violent and abusive and it wasn't until Zimbardo's girlfriend and fellow psych researcher freaked out that the experiment was abruptly halted (after only one of the two planned weeks had been completed). Zimbardo uses his learnings from the SPE to help understand how horrors like Abu Ghraib, Darfur, and the Holocaust happen. The book challenges conventional thinking around the idea of free will. While we instinctively believe that we independently govern our own behavior, Zimbardo convincingly demonstrates how "the situation" dramatically influences your actions. While it's very hard to accept that you (yes you) could act terribly given the right pressures and environment you'd be hard pressed after reading this book to maintain that you're somehow immune.
While Zimbardo didn't write his book specifically for leaders/managers his work carries a valuable lesson. We the creators of the systems in which people work, live, and play, are responsible for systemic behaviors within our organizations. Placing blame for misdeeds primarily on "bad apples" (which is what the military effectively did with Abu Ghraib) is misguided when there is evidence of systemic problems (a "bad barrel"). The incentives we put in place, the small things we ignore, all send important signals through the chain of command. It's our duty to sweat the details and make sure the emergent behaviors at the other end are ones we're be proud of.