NEW YORK - "When you play the game of thrones, you win or you die. There is no middle ground." That's a line from "Game of Thrones," the popular HBO television series based on a best-selling series of books.But it could just as easily refer to the no-holds-barred battles we are watching in Libya and Syria. What is hardest to grasp is how these regimes are both strong and brittle. Their rulers are ruthless dictators prepared to do whatever it takes to stay in power -- and for decades that can work.Until, suddenly, it does not.We are not very good at understanding the win-or-die dynamic of these sorts of political systems: Not so long ago, everyone from the U.S. State Department, to Harvard, to the London School of Economics, to Vogue magazine, to blue-chip Wall Street money managers treated the Assads and the Gaddafis like rulers capable of gradual liberalization and even democratization.Part of the problem is that the Cold War habit of mind, with its division of the world into two rival, ideologically cohesive camps, dies hard. Its legacy today is our tendency to look for a new, black-and-white division, this time into democracies and dictatorships. (Remember the "Axis of Evil.")But modern dictatorships come in many different varieties. The ones that are collapsing in the Middle East are examples of what political scientists call "sultanistic" dictatorships.According to Jack Goldstone, a professor at the School of Public Policy at George Mason University in Virginia, the defining characteristic of a sultanistic regime is that it has no purpose apart from maintaining the leader's personal authority. "A sultanistic regime is one in which the leader of a country has managed to gain control of all the levers of state power," Goldstone said. "No one has any secure rights, and the leader rules with absolute authority."Richard Snyder, a professor of political science at Brown University in Rhode Island, said sultanistic regimes, which he prefers to call "personalistic dictatorships" or "neo-patrimonial dictatorships," are all about the guy on top. "People get goodies for being close to the ruler. That's the essence of it," he told me.Sultans establish their power by making sure no one else has any -- or at least any that is independent of the sultan himself. That means that sultans intentionally hollow out their own government institutions."Autocrats in these cases consciously weaken the state, both by filling it with cronies picked more for loyalty than competence and by starving those parts of it not controlled by close allies," said Lucan Way, a professor of political science at the University of Toronto. "Thus, in Libya, Muammar Gaddafi severely underfunded the military while ensuring that his sons commanded the most highly trained and best-equipped militias."Successful sultans, Goldstone said, also work to make and to keep their societies divided: "The ideal arrangement is to be supported by many elite groups, none of which are inclined to support one another."All of which makes sultanistic regimes particularly awful places to live. The bitter and corrosive sense of personal humiliation that inspired so many participants in the Arab Spring was not accidental -- it is central to how sultanism works. "Under a sultanistic regime, because nobody has any rights, they all feel humiliated and subject to the whims of the ruler," Goldstone said.But modern-day sultans have an Achilles' heel. The techniques they use to establish and maintain power make them very, very strong when they are in charge -- Goldstone said that sultans have more personal authority than medieval monarchs did -- but they also make their regimes extremely brittle. If a revolution starts, it can succeed swiftly."The regime's supporters are not motivated by any real animating or guiding philosophy," Snyder said. "It is not like fundamentalist Islam or communism.""The armed forces need to decide: 'How many of our own people do we need to shoot to keep the boss in power,'" Goldstone said. "If the boss looks strong, the whole regime looks strong. But if the boss starts to look weak, it crumples fairly quickly."That is the good news. The bad news is that the brittleness of sultanistic regimes is a mixed blessing -- it helps the revolutionaries when they are in the streets, but it complicates the task of nation-building after they win.A smart dictator of a sultanistic regime eviscerates his country's institutions; rules by personal fiat, not by law; and creates a divided society in which sycophancy and corruption are the paths to prosperity. Citizens of such societies lack even a shared set of values -- they live in what Mr. Snyder called "a belief vacuum."That is why it will be neither a failure nor a betrayal if the best the Libyan rebels manage to establish is a weak democracy that is unstable, divided and inefficient. Effective democracies take generations to build. They are the opposite of sultanistic regimes: hard to establish, internally complex and querulous -- but enduring.You do not need a degree in political science to figure that out. Daenerys, one of the heroines of the George Martin fantasy series on which HBO's TV serial is based, discovers that overthrowing the cruel, slave-owning oligarchies that run a troika of city-states is surprisingly easy. But she despairs when the regimes that replace them turn out to be little better.It is easy to cheer the fall of the sultanistic dictatorships. Now is the moment to remember to be patient when their humiliated and divided people find it is a struggle to build a government that is not quite so bad.