President Ali Abdullah Saleh’s 32-year reign in Yemen is over, and the Middle East revolution has deposed its third dictator, his opponents claim.

Not so, says the US-backed Yemeni strongman, who yesterday warned that Yemen will descend into bloody civil war — just like Libya — if his opponents try to depose him.

Either way, the next 24 hours could be crucial. More than half the Yemeni army and at least six of its top generals have defected to the protesters, and forces from opposing sides are now drawn up in the capital Sana’a.

Yesterday, at least four people were killed in flare-ups between pro- and anti-Saleh forces in southern Yemen as the standoff continued.

A dozen tanks from Al-Saleh’s Republican Guard are guarding the presidential palace in Sana’a, while tanks commanded by Saleh’s half brother, General Ali Mohsen Saleh — who joined the opposition on Sunday — are shielding protesters in Taghyeer Square and keeping an eye on the central bank and TV station.

An unnamed US official told the Washington Post it was a miracle the president had survived through Monday. Meanwhile, the editor-in-chief of the Yemen Post told Al Jazeera that Saleh’s reign was “officially over” now that 60% of the army had joined the protesters. The bookies at Intrade this morning give Saleh a 1-in-5 chance of remaining in power until the end of the year, which is better odds than yesterday — for him, at least.

This showdown in Yemen’s six-week long protest was precipitated by pro-government snipers firing on protesters in Taghyeer Square last Friday, killing 52 people.

Two days later, tens of thousands of demonstrators came back to the square for the funerals, promising that the martyrs’ blood would not be spilt in vain.

By then, Saleh’s supporters were deserting en masse, with Yemen’s ambassadors to at least 19 different countries quitting their posts and dozens of army officers (and key tribal leaders) joining the opposition.

The most valuable recruit for the protesters was General Ali Mohsen, chief of the north-west military region, commander of a tank division and Yemen’s second most powerful man. Often described as Saleh’s “iron fist”, he is now well placed to become Yemen’s king maker, if not actually its king.

In 2005, former US ambassador Thomas Krajeski described Mohsen in a cable to Washington (released by WikiLeaks) as an Islamist who had made a fortune from smuggling arms, diesel, food and consumer goods.

Krajeski reported that the general was not his preferred choice as President Saleh’s successor:

“Ali Mohsen’s questionable dealings with terrorists and extremists … would make his accession unwelcome to the US and others in the international community … He is known to have Salafi leanings and to support a more radical Islamic political agenda than Saleh.”

So who cares what happens and why does it matter? Yemen is the poorest country in the Middle East and has very little oil. More than half its 23 million people are illiterate and 40% live below the poverty line. It’s also been a failed state for years.

Well, the United States cares, for starters. President Saleh has been a key ally in America’s fight against al-Qaeda in the Arabian Peninsula (AQAP) and Yemen is believed to be a major AQAP base. Eleven years ago 17 US personnel were killed in a suicide attack on the USS Cole in the port of Aden. In 2008, another 18 people were killed in an attack on the US Embassy in Sana’a. And in December 2009, Yemeni al-Qaeda supporters claimed responsibility for the attempted bombing of a Detroit-bound US airliner. Even more recently, Yemeni bombs were found on cargo planes flying to the US last October.

Currently, US Special Forces train the Yemeni army (which is largely run by President Saleh’s extended family) and Yemen allows US drones to bomb AQAP targets while pretending that its own forces are making the attacks.

Yemen’s next government — if Saleh goes — might not be nearly so co-operative in the fight against terrorism.

Yemen’s next-door neighbour, Saudi Arabia, is also worried about AQAP and what happens if Saleh goes. The Saudis share a border with Yemen, populated by rebellious Shi’ite tribes, who might cause fresh trouble if Yemen starts falling apart. But their biggest concern would be another victory for democracy and people power, (if that’s possible in a country so beset by tribal and regional divisions).

Yesterday, President Saleh sent his foreign minister to Riyadh to deliver a letter to King Abdullah. According to the US-based Stratfor website: Saleh is likely asking for Saudi support for his regime, making the case that his downfall will lead to a fracturing of the country and greater instability for the Arabian Peninsula overall. Saudi support for Saleh is nowhere near assured, however.

Ten days ago, Saudi Arabia sent its soldiers across the causeway into neighbouring Bahrain to help put down that country’s democracy movement. But it won’t be so easy to march into Yemen, and not just because it’s logistically difficult. Half the Yemeni army could be standing in the way of any such move.

Last but not least in the ranks of who cares are Yemen’s young pro-democracy protesters. Their natural fear — which may well be justified — is that the face of the regime will change but its nature will remain the same.

That outcome would surely suit the US and the Saudis, if they could engineer such a solution.

In the meantime, a Libyan-style civil war is a distinct possibility. The country has had several major conflicts in the past 50 years — it was two nations till 1990 — and is still deeply divided between north and south. President Saleh has managed to survive them all and seems sure he could survive another.

Saleh told protesters yesterday he would be prepared to quit in early 2012, once elections are arranged. His opponents turned him down, saying he has broken such promises before and can’t be trusted to do so again.

Watch this space.