Thousands of Algerians poured into the streets Tuesday, and Americans should watch carefully as Arab Spring 2.0 threatens to wreak havoc on North Africa and beyond.

The uprising first erupted three weeks ago, after President ­Abdelaziz Bouteflika announced his intention to run for re-election on April 18. The 82-year-old has been in power for 20 years, but for a decade Algerians have hardly heard his voice or seen his picture.

A coterie of nameless and unaccountable generals, businessmen, and bureaucrats have been running the country — and have made a hash of it. ­Unemployment runs high, especially among young people, who comprise a majority of the population. A sluggish economy combined with a youth bulge is a recipe for disaster.

Mr. Bouteflika, who’d flown to Geneva for medical treatment, returned to his country on Sunday. Rare footage showed him being whisked through the airport in a wheelchair, “Weekend at Bernie’s” style.

On Monday, he announced he wouldn’t run after all. Instead, the election was postponed for next year, extending his rule until an unspecified date. Rather than ending the protests, his move only added fuel to the fire. Will the flames remain confined to Algeria?

In 2010 a Tunisian street vendor set himself on fire after he was humiliated by the police. His self-immolation triggered a decade of Arab unrest. Instead of ushering democracy to the region, however, the first Arab Spring wrought Islamist takeovers, failed states, and civil war.

Since then, the region’s wars have killed nearly a million people. Refugees have flooded Europe. A new Islamist group, ISIS, created a “caliphate” stretching across the Levant and Mesopotamia. It was a ruinous “spring.”

America, tired of being a world policeman for a century, tried in vain to stay out — and when President Barack Obama finally did intervene, helping to overthrow Muammar Kadhafi, we didn’t do too well. Today’s Libya remains an anarchic breeding ground for extremists. Also, after withdrawing from Iraq, American troops had to return to fight ISIS. President Trump walked back his recent decision to withdraw all troops from Syria.

Mideast fatigue notwithstanding, can we afford to ignore a potential new phase of Arab unrest?

True, Algeria may well be a unique case. Mr. Bouteflika managed to escape the fate of his fellow dictators last time around. That’s not least because a brutal civil war between the army and Islamists in the 1990s scarred the Algerian psyche.

The Algerian street scenes, though, demonstrate that unaccountable Arab “republics” are fragile. Arab kingdoms — Jordan, Saudi Arabia, the United Arab Emirates, Morocco — managed to steer through this decade’s mayhem better than did the republics. A new generation of fairly young kings is more attuned to street wishes than their “elected” brethren, but even they experience periodic unrest.

Algeria’s rebellion can end up resembling the killing fields of Libya, Syria, and Yemen. Then again, today’s Tunisia is a hopeful model for some kind of spring, complete with an elected, accountable government. The Islamist party there, Ennahda, has renounced political Islam, and the Tunisian constitution Ennahda has signed onto is the most liberal in the Arab world. Tunisia’s spring, though, may not last.

Other Islamists, like the Muslim Brotherhood, represent the more dangerous course.

In Egypt, America supported an elected Brotherhood government just to see it fail so spectacularly that Egyptians cheered its overthrow in a military coup, complete with a return to strongman dictatorship under Abdel Fatah al-Sisi. In Gaza, a Brotherhood offshoot, Hamas, traps the population.

With all these confusing trends, what’s America to do?

Don’t write a blank check to repressive regimes. As Jonathan Schanzer of the Foundation for Defense of Democracies tells it, these regimes breed terrorism, extremism, and instability. At the same time, Washington can’t “embrace a full revolution.” Instead, America should push sustainable reform. Mideast ­involvement is “out of vogue at the moment, but that doesn’t mean it’s not our best option.”

So, yes, polls show Americans would rather ignore it all. Still, Washington has enough leverage over Algiers to nudge its rulers to better listen to the streets and enact reforms. The alternative — revolution, civil war, continued repression, Islamist overtake, new terrorist groups — risks future trouble.

And it won’t be confined to North Africa.

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Twitter: @BennyAvni. From the New York Post.