As Libyan rebels seize Tripoli, it’s a ripe moment to reconsider the mythology of the Arab Spring.

The Libyan rebels, like those in Tunisia and Egypt, have shown that the rule of Mideast despots will no longer go uncontested. But this cri de coeur by discontented youth doesn’t guarantee that new democracies will emerge.

The springtime burst of optimism after the fall of autocrats in Cairo and Tunis was followed by a bloody summer in Libya and Syria. Despite the contagious explosion of popular frustration that swept most Arab nations, their prospects for positive change in the short term are slim.

For most, full blown democracy will take years, or decades, to achieve.

Judging from developments in Tunisia, Egypt, Syria, and Libya, most Arab revolts share one thing in common. Those Arabs with the most open-minded, tolerant vision of change are having difficulty forming cohesive political movements. Islamists and remnants of the old guard seem better able to organize and have greater financial resources.

Libya — a country with almost no functioning institutions after 42 years of Moammar Gadhafi’s bizarre rule — will have a hard time bucking that trend.

At this point, we know very little about who will wind up governing Libya. The Benghazi-based opposition leadership known as the National Transitional Council has been recognized by the United States and many other governments as Libya’s ruling body; it is composed of exiled technocrats and former Gadhafi officials.

But rebels from other areas of Libya are wary of the NTC, and there are sharp divisions within it. It will have to add representatives from different regions and multiple tribes if it wants to unite the country behind it. It must also figure out how to incorporate former Gadhafi loyalists into the new system, lest they turn into armed insurgents, as happened with former Saddam loyalists in Iraq.

The challenge is mind-boggling. The NTC must rebuild the Libyan state from the bottom. NATO countries, in particular Britain and France, stand ready to help. But they, and the United States, have to be wary of undercutting the new government’s legitimacy. Already, NATO’s military support for the rebels — so crucial to their victory — has caused Arab Islamists to label them as puppets.

This raises another crucial unknown: what role Islamists will play in Libya’s fate.

Some years ago, Gadhafi crushed Libyan jihadists from the Libyan Islamic Fighting Group, who had been affiliated with al-Qaeda. But last year, as part of a government rehabilitation program, he released many of these fighters, who have taken an active role in the rebellion. One Islamist rebel leader is blamed for the recent assassination of Abdel-Fatah Younis, the former rebel military commander.

If a new Libyan government alienates tribes or regional factions, Islamists will profit from their anger. On the plus side, Libya has huge oil resources and a small population, so even a weak or ineffectual government may be able to buy off the discontented. Or it may not.

In Tunisia and Egypt, Libya’s two neighbors, governments don’t have such oil resources. Hit by a postrevolution collapse of tourism and trade, they suffer from high unemployment. The Arab Spring generated huge hopes among youth that their lives would get better. These hopes are, as yet, unmet.

If Libya’s economy rebounds, one million Egyptians and 400,000 Tunisians who worked in Libya before its revolution may regain their jobs. That would help tamp down economic frustrations, but not enough to appease rising expectations.

Islamic political parties, with their many social-service programs, stand ready to capitalize on this discontent, even as a multitude of liberal parties in Tunis and Cairo fail to gain traction. The youthful Facebook organizers who proved so adept at rallying crowds to oppose their rulers have yet to figure out how to rally voters to their views.

In Syria, too, the brave rebels confronting the regime’s bullets have no broad organization. Many are secular, but Syrian President Bashar al-Assad long ago squashed all secular opposition groups and their leaders. This guarantees that the strongest organized opposition on the ground will originate in the mosque.

The victory of the Libyan opposition may reinvigorate the morale of many Arab rebels (although it’s likely to persuade Syria’s Assad to crack down even harder). Yet this victory shouldn’t delude us. We must recognize that those who struggle for Arab democracy will face a chilly fall and winter before they reach spring.