There is a second Arab Spring in the air in North Africa. In Algeria and Sudan, two of the most miserably repressive dictators on the African continent have fallen to popular protests. That sounds hopeful — but we know the catastrophes the first Arab Spring brought after 2011. The second Spring promises worse.

The removal of the Algerian and Sudanese dictators was preceded by signs that are clear in retrospect. Most obviously, both were long-serving: Algeria’s Abdelaziz Bouteflika had been in charge since 1999, Sudan’s Omar al-Bashir since 1989.

Even more telling are the demographic similarities. Both nations have a young population — 41 percent under 15 in Sudan, 44 percent under 25 in Algeria. As a result of regime corruption and repression, combined with their baby booms, both have high youth unemployment. Finally, both pump enough oil to buy off protests when prices are high — but not enough to stay rich when prices fall.

Sudan attracts more attention in the West, thanks to its genocidal conduct in Darfur and the low-level war it waged for a decade with the new nation of South Sudan. But Algeria is more significant.

This isn’t because of its inherent importance. Algeria is only the 18th largest oil producer in the world. Its trackless southern border with Mauritania, Mali, and Niger is purely nominal, but the United States has no significant interests in any of these nations. Algeria matters not for its strength, but for its weakness.

In 1992, an Islamist party won major victories in regional Algerian elections. This prompted the army to annul the elections and fight a victorious civil war against the Islamists that laid the foundations for the Bouteflika regime.

The United States missed the significance of that Islamist challenge. In those years, the Taliban was rising to power in Afghanistan, and Saddam Hussein was turning to Islam as his justification for ruling Iraq. In retrospect, the Algerian civil war foretold the wave of violence that broke on 9/11.

But at the time, the civil war mattered mostly to Algeria itself, and to France. To say that France and Algeria have a complex history hardly does their relationship justice. After 1830, Algeria was not, legally speaking, a colony in the French Empire: it was administered as part of France itself.

The Algerian war for independence (1954-1962) was a challenge to the French Fourth Republic, which collapsed under the strain. Gen. Charles de Gaulle established today’s French Republic, and in 1962 was nearly assassinated after he accepted Algerian independence.

But for reasons of geography and history, the ties between France and Algeria remained close. During the Algerian civil war, tens of thousands of Algerians fled to France. The risk of the overthrow of the Algerian regime is that this flight will be renewed — this time, by hundreds of thousands.

We can hope that Algeria will miraculously stabilize. Certainly the experience of the civil war offers a warning. The fact that the protests against Bouteflika were peaceful offers hope that the protesters have learned the lesson that neither the Islamists nor the military have any useful answers.

But Algeria has no meaningful experience with democracy. While Bouteflika is gone, his regime remains: the potential for a crackdown is real. Algeria’s young population has known only civil war and dictatorship. Its economy is weak. The seeds of Islamism were sown in the 1970s. And France is prosperous, home to a million Algerians, and just across a narrow sea.

The first Arab Spring led to the migration of several million Syrians and other peoples into Europe. Unless the Europeans act to prevent it, this Arab Spring may shake not North Africa, but Paris.