The Middle East is a political outlier, the world’s least hospitable place for liberal democracy. But as popular demands for freedom spread virally across the region, they are illuminating a varied political landscape, not just monolithic tyranny.

Think of it as a continuum of despotism. On the “soft” end are Tunisia and Egypt, where longtime strongmen were ousted with surprising ease. Mostly nonviolent popular protests were sufficient to shove them into involuntary retirement.

On the “hard” end is Libya’s Muammar Qaddafi. Unlike Hosni Mubarak or Zine el-Abidine Ben Ali, the self-anointed “Brother Leader” has shown no compunction about massacring his own people to hold onto power. While rebels are fighting back valiantly, it could take a hard shove from the outside world to topple hardcore tyrants like Qaddafi.

In any case, the popular uprisings are sorting out where the region’s countries fall along the autocratic continuum. It’s also shedding light on the conditions that make some countries more receptive to political change than others.

A month ago, there didn’t seem to be anything particularly “soft” about Mubarak and Ben Ali. They were essentially dictators who ruled by decree, clamped down hard on political opponents, routinely violated basic human rights, including torturing prisoners, and tolerated pervasive corruption and cronyism.

Yet, to invoke Jeanne Kirpatrick’s famous Cold War-era dichotomy, they were authoritarians rather than totalitarians. They depended on the tacit support of respected national institutions like the army, as well as governing and economic elites who preferred “stability” to the hazards of open political competition. When the uprisings made it clear that the heretofore voiceless masses had turned against the rulers, that support quickly evaporated and they had little choice but to step down.

In contrast, the megalomaniacal Qaddafi has ruled absolutely for 42 years. Rather than use Libya’s oil and gas wealth to develop and modernize the country’s economy, he funneled much of it into overseas intrigues, including several vicious civil conflicts in Africa. Libya remains a highly tribal society where national institutions (including the army), private markets and civil society – key building blocks for democracy – are weak.

In general, America’s friends and allies in the Middle East are mostly grouped toward the soft end of the despotic continuum, while our adversaries congregate at the hard end. This should surprise no one except for foreign policy “realists,” who reject the idea that the internal political structures of countries have any effect on their conduct abroad. Yet it can hardly be a coincidence that the least open societies and most illiberal regimes in the region – Libya, Syria, Iran, and Iraq before 2003 – are the most likely to foment terrorism, chase after nuclear weapons, reject Israel’s existence, and brutally oppress their own people.

That Syria hasn’t seen much unrest is surely related to the fact that it’s a thoroughly nasty police state run by hereditary dictator Bashar al-Assad, whose father, Hafez al-Assad, leveled the rebellious city of Hama in 1982, at the cost of over 17,000 lives. Iran’s Green Movement has managed a few small protests in solidarity with the Arab revolt, but has been mostly kept under wraps by the Islamic Republic’s thuggish security organs.

With the exception of Bahrain, the region’s monarchies also have dodged the revolutionary bullet – so far. Arab kings evidently enjoy a greater degree of legitimacy and popular acceptance than secular strongmen. King Abdullah II of Jordan and King Mohammed V of Morocco have proven adept at creating at least a façade of parliamentary rule and at displacing popular anger onto governments they can dismiss from time to time to appease public wrath. Nonetheless, Washington should nudge such “liberal autocracies” to go beyond cosmetic reforms, lest they be engulfed by the rising revolutionary tide.

The country that really has U.S. policy-makers holding their breath, of course, is Saudi Arabia. It falls somewhere in the middle of the autocratic continuum. On the one hand, they’ve been U.S. allies since FDR’s day, sit atop oil reserves vital to America’s auto-centric culture and share our interest in destroying al Qaeda. On the other hand, Saudi Arabia is a run by a deeply illiberal monarchy that enforces Sharia law, uses its oil wealth to export Wahabbist fundamentalism, and relegates women to second-class status. The appearance of a serious pro-democracy movement there would force Americans to face these contradictions and rethink our close ties with the ruling family.

The Middle East’s variegated political landscape offers grounds for measured hope about prospects for liberal democracy. Political and economic freedom will likely advance fitfully and partially in some places, hardly at all in others. There will be slippage and backsliding. But there’s a striking opportunity for the United States to nudge its friends and allies further toward the “soft” end of the despotic continuum, and eventually off it altogether.