DJERBA, Tunisia — The idealism of the revolts in Egypt and Tunisia, where the power of the street revealed the frailty of authority, revived an Arab world anticipating change. But Libya’s unfinished revolution, as inspiring as it is unsettling, illustrates how perilous that change has become as it unfolds in this phase of the Arab Spring.

Though the rebels’ flag has gone up in Tripoli, their leadership is fractured and opaque; the intentions and influence of Islamists in their ranks are uncertain; Col. Muammar el-Qaddafi remains at large in a flight reminiscent of Saddam Hussein’s; and foreigners have been involved in the fight in the kind of intervention that has long been toxic to the Arab world.

Not to mention, of course, that a lot of young men have a lot of guns.

No uprising is alike, but Libya’s complexities echo in the revolts in Bahrain, Syria and, most of all, Yemen, suggesting that the prolonged transition of Arab countries to a new order may prove as tumultuous to the region as Egypt’s moment was stirring.

Unlike at the start of the year, when the revolutionary momentum seemed unstoppable, uncertainty is far more pronounced today, as several countries face the prospect of stalemate, sustained conflict or power vacuums that may render them ungovernable. Already in Yemen, militant Islamists have found a haven. Across the region, the repercussions of the uprisings are colliding with the assumptions of the older, American-backed system: control of oil, the influence of a reactionary Saudi Arabia, an Arab-Israeli truce, and the maintenance of order at the expense of freedom in a region that for decades has been, at least superficially, one of the world’s most stable.