For 18 years, Bruce Bueno de  Mesquita and Alastair Smith have been revolutionizing the study of  politics by turning conventional wisdom on its head. They start from a  single assertion: Leaders do whatever keeps them in power. They don't  care about the "national interest" - or even their subjects - unless  they have to.

This clever and accessible book shows that the difference between  tyrants and democrats is just a convenient fiction. Governments do not  differ in kind but only in the number of essential supporters, or backs  that need scratching. The size of this group determines almost  everything about politics: what leaders can get away with, and the  quality of life or misery under them. The picture the authors paint is  not pretty. But it just may be the truth, which is a good starting point  for anyone seeking to improve human governance.