Earlier this week, in what appeared be a desperate attempt to remain in power, Yemeni President Ali Abdullah Saleh unleashed his guns on Sadiq al-Ahmar, leader of the powerful Hashid tribal confederation. Ahmar's gunmen in the Hasaba district of northern Sana'a appear to be holding their ground against the military's attempts to dislodge them; meanwhile, thousands of tribal reinforcements are fighting their way toward the capital from Amran, the heart of Hashid tribal territory, although they were stopped by Saleh's military on Friday.

Saleh's resort to violence represents more finely calculated politics than, for example, the desperate and vengeful attacks of Libya's Muammar al-Qaddafi. By transforming the conflict from a popular people's protest movement against an autocratic leader into a military conflict between the state and leading tribal rivals, Saleh may be positioning himself and his family to remain key players in Yemen.

Hashid and Bakil are the two large tribal confederations in north Yemen that historically have been important sources of power in the country. Tribal federations are groupings of tribes, but they are loose and do not resemble a command structure. A tribal leader's power is contingent on the circumstances of the moment, and he is only powerful if his rallying cry resonates with tribesmen. Yemen's tribesmen are individuals first, concerned with their own honor and survival: If their neighbor is gaining influence, they will look for anybody who can help restore the relative balance of power, regardless of politics or ideology.

In the twentieth century, Hashid and Bakil came into particular prominence in Yemeni politics. Under Yahya, a Zaydi imam, in the first half of the twentieth century, Bakil and Hashid were known as the imam's "wings." In 1962, when Egyptian-backed Yemeni republicans overthrew the imamate, the northern tribes divided between royalists and republicans and fought a long civil war. A military stalemate eventually allowed the republic to survive. But in the process, the war empowered the northern tribes that were well supplied with weapons from competing Cold War patrons. Tribal sheikhs strengthened their own power bases and used them to extend their power over the national government itself. When the government tried to marginalize the sheikhs in the mid-1970s, tribal fighters surrounded the capital, and the president, Ibrahim al-Hamdi, was killed. Although Saleh himself was in the military at the time (he was a commander of the garrison at Taizz), he sided with the tribal sheikhs and took power himself shortly afterward. That is why Saleh's attack on Hashid today seems so bold: By opposing the tribes, he is tempting the same fate as Hamdi.

Since Hamdi's assassination, Saleh has shared the most powerful positions in Yemen with the Hashid tribal federation. Until his death in 2007, the Hashid were led by Abdullah bin Hussein al-Ahmar, who served as speaker of the Yemeni parliament. (Sadiq al-Ahmar, the current leader, is his oldest son.) When political parties were legalized in 1990, he emerged as the leader of the Islah party, a coalition of Muslim Brotherhood ideologues, Ahmar's Hashid tribes, and anti-communist merchants. Saleh and Ahmar were strong allies: Over the years, they jointly fought the communist People's Democratic Republic of Yemen, the communist-inspired National Liberation Front in the early 1980s, the Yemeni Socialist Party in the civil war of 1994, and lastly, the Houthi rebellion in the north over the past decade.

The Houthis are a family of prominent Zaydi Shiite scholars in Yemen who led a revolt of tribesmen, Zaydi elite, and many others disgruntled with Saleh's rule in the northern-most governorate in Yemen, Sa'adah. The revolt flared on and off from 2004 until 2010, when the Yemeni regime and the Saudi military launched a scorched-earth campaign to destroy the Houthis. The Houthi fighters held both the Saudi and Yemeni militaries at bay. The ensuing truce has held largely because the Houthis have since been left to run their affairs in Sa'adah.

In 1997, Saleh's ruling party broke with the Islah party, because the president wanted to distance himself from his most powerful allies and most potent rivals, the Islamists. At that point, Islah transformed itself into an opposition party. Although Saleh's ruling party and Ahmar's Islah fought over elections and contested each other for power, they always had certain shared ground, for example, against the Houthi movement in the north or against the secessionists in the south. Today, the two have broken into an inter-elite struggle: Islah is the main power behind the coalition of traditional opposition parties leading the negotiations for the protesters with the Gulf Cooperation Council.

Although Saleh's assault on Ahmar's compound in Hasaba may have been intended only to humiliate and subdue the Hashid leadership, Saleh might have miscalculated the risk of a much wider revolt and civil conflict. Already, back in March, in Marib, an area in Yemen's east rich in oil and natural gas, the tribes blew up crucial oil pipelines and electrical generation plants in solidarity with the peaceful protest movement. By paralyzing Yemen's oil exports, which represent 30 percent of GDP and 75 percent of state revenue over the last decade, the Abida in Marib managed to achieve what al Qaeda could only dream of: cutting the economic Achilles heel of Yemen.

Meanwhile, the Islahi-affiliated Qar'an and Jad'an tribes in Marib overran the base of the 26th Brigade of the Republican Guard at Fardha Mountain, which overlooks the strategic pass between Sana'a and the east. On Wednesday, thousands of Hashid tribesmen from Amran, northwest of Sana'a, battled military units at the northern checkpoint of the capital, attempting to join the defense of Ahmar. The battle inside Sana'a is going badly for the government, as well. Ahmar's Hashid fighters have taken a number of important government buildings, including the ruling party headquarters.

Saleh has long portrayed the movement against him as a "coup," and in his view, Hamid al-Ahmar, one of Sadiq's younger brothers, is the primary instigator, along with General Ali Muhsin al-Ahmar and Saudi Arabia, the Ahmars' biggest benefactor. In Saleh's view, eliminating the coup leaders would then make sense: Without them, the peaceful protesters could easily be negotiated with or outwitted. For most of the last months of protests, it suited Saleh to avoid violence and invite the demonstrators to channel their demands in the form of an electoral campaign. Saleh is happy with elections, because he knows that the protesters and the opposition are divided and that his best hopes are for them to self-destruct.

But the peace did not hold. On March 18, irregular supporters of the regime -- perhaps someone inside the government trying to force the issue -- organized a massacre of protesters near Sana'a University. The violence escalated, and as the United States, Europe, and the Gulf Cooperation Council saw Saleh losing control, they all turned against him, calling for his removal. For its part, the GCC created a plan with the United States' blessing that would have retired Saleh to a house in Jeddah. Now, with nowhere to turn, Saleh is trying to play his advantage by dragging the political conflict into a military conflict, at which he is a master.

Yet this may not be an act of desperation. Saleh appears confident that he can provoke a war with the Hashid leadership and escape unharmed. This is partly because the tribes themselves are weakening. Hashid's position, in particular, has been slipping since the war with the Houthis began in 2004 and has only accelerated after the death of Abdullah bin Hussein al-Ahmar. Hashid fighters were routed by the Houthis, the new power in the north. The Houthis are extending their power eastward and southward by making tribal alliances, worrying Saudi Arabia because the leadership is comprised of Zaydi Shiites, and the Saudis fear Iranian influence (although there is little evidence of this). Since 2004, the Saudis had supported the Hashid as a proxy force against the Houthis, but now, with the Hashid's effectiveness in question, Riyadh is reevaluating the worth of their Yemeni clients. The Saudis have increased their ties with Al-Ukaimi bin al-Jawf, a Bakil sheikh also associated with the Islah party, as a result.

The Houthis have also achieved this success by exploiting the resentments of tribesmen toward their traditional leadership. The last 20 years have seen the rise of the "city sheikh," or the sheikh who is a member of parliament or a military commander and defends tribes and tribalism in the national government, but who has often lost touch with the issues of tribesmen in rural areas. The Houthis, however, are perceived to be more grounded in local needs than Yemen's traditional tribal powerbrokers. This sense of grievance is also a reason why many tribesmen have abandoned their tribal areas and weapons to come join the protestors in Sana’a, and why religious and political parties have made deep inroads into tribal areas.

Finally, and most critically for the immediate military outcome of the fighting, tribes are intensely local organizations that are concerned only with their immediate geographic area. They are not motivated by politics or ideology but by practical considerations of the local power balance among other tribes. As such, tribal society is deeply fractured and impossible to unite: The tribes will inevitably battle among themselves.

The second-most powerful group in Hashid led by Sheikh Jalidan is a supporter of Saleh. In May, when the Ahmar brothers announced the resignation of Hussein al-Ahmar from Saleh's ruling party and the joining of Hashid and Bakil tribes with the protesters, the brothers could not get to their own rally in Amran because tribes supporting the government had cut the roads. Saleh still enjoys a good deal of support from tribes alienated from the Ahmar leadership and those loyal to him for his support against their local enemies.

As long as Saleh remains a power to be reckoned with, local tribes will be willing to give loyalty in exchange for support in some local concern. By confronting the Hashid leadership, Saleh may just yet undermine the protesters, effectively converting Yemen's troubles into an elite struggle over state leadership -- a "coup" against law and order, to use Saleh's word. He will become a power without whom Yemen's wars are insolvable, thereby guaranteeing himself a role in the country's future -- if, that is, he survives his own war.