Violence is rooted in the flawed 1943 power-sharing pact.

Beirut, Lebanon - Huddled at home in front of their TVs during last week's fighting, the Lebanese relived one of their worst memories: masked gunmen setting up makeshift checkpoints and demanding people's identity cards. The image of gunmen stopping civilians at checkpoints to sort and often murder them on the basis of religion is perhaps the most enduring symbol of Lebanon's 15-year civil war.

During that war, the sectarian divide was between Muslims and Christians. This time, the conflict is mainly between Sunnis and Shiites. It is also an extension of the ongoing proxy war in Iraq – pitting Iran and Syria (which support the Shiite militia Hezbollah) against the United States, Saudi Arabia, and other Sunni Arab regimes (which back Lebanon's Sunni- and Christian-dominated government).

Each Lebanese faction accuses the other of serving external masters. Hezbollah claims the US put the ruling coalition up to issuing two recent orders: one outlawing the militia's private communications network and another dismissing the security chief at the Beirut airport. In turn, the government accuses Hezbollah of carrying out a "coup" at the behest of Iran and Syria.

But while external players have a hand in the latest bloody confrontations, they don't deserve all the blame. For the most part, the Lebanese did this to themselves – and they need to find a political settlement of their own by modernizing an antiquated power-sharing system. Otherwise, the Sunni-Shiite rift in Lebanon will explode, especially since it has been fueled by years of sectarian bloodletting in Iraq. TV stations showing pictures of mutilated bodies, rumors of forced evacuations on both sides, and a gunman opening fire on a funeral – these sound like scenes from Iraq, but now they're taking place in Lebanon.

On May 9, Hezbollah dispatched hundreds of heavily armed fighters into West Beirut, and they quickly routed Sunni militiamen, took control of their political offices, and shut down media outlets owned by the Sunni leader Saad Hariri (son of former Prime Minister Rafik Hariri, assassinated in 2005). The US-allied government of Prime Minister Fouad Siniora appeared powerless, while the Lebanese Army stood on the sidelines. On May 15, the government rescinded its orders, Hezbollah pulled its fighters off the streets, and leaders of the two factions headed to Qatar to negotiate.

The standoff in Lebanon is extremely dangerous, and a political settlement will be difficult. The country has been without a president since November, when Syrian ally Emile Lahoud's term ended. Since then, the two opposing factions – a parliamentary majority led by Mr. Hariri, and an opposition led by Hezbollah and its Maronite Christian ally Michel Aoun – agreed on Gen. Michel Suleiman, head of the Lebanese Army, as a compromise for president. But the two blocs have failed to agree on the makeup of a new cabinet, and the parliamentary vote to choose a new president has been postponed 19 times.

The paralysis actually began in November 2006, when six ministers representing Hezbollah and its allies resigned from Mr. Siniora's cabinet. Hezbollah and Mr. Aoun then launched an ongoing protest in downtown Beirut.

Today, Lebanon's crises are interconnected – the pressure on Hezbollah to give up its weapons, the need to agree on a new electoral law before parliamentary elections in 2009, the country's future relationship with Syria, and the disarming of various factions in 12 Palestinian refugee camps scattered across the country.

Lebanon's problems are rooted in a 1943 power-sharing agreement installed when the country won its independence from French colonial rule. The system was designed to keep a balance among 18 religious sects, dividing power between a Maronite president, a Sunni prime minister, and a Shiite speaker of parliament. This system extends from the top ranks of government to the lowest rungs of civil service jobs, and has barely changed since it was put in place 65 years ago.

When civil war broke out in 1975, the political imbalance helped drive the major sects to form their own militias. Because of the confessional system, Lebanese political institutions never got a chance to develop; the country remained dependent on the powerful clans and feudal landlords that held sway in much of Lebanon. The zaeem, or confessional leader who usually inherited rule from his father, became paramount during the war.

Confessionalism leads to a weak state. It encourages horse-trading and alliances with powerful patrons. And it is easily exploited by outside powers. But most of the current players are too invested in this system to really change it. And foreign patrons do not want change, because that could reduce their influence.

Even if the two factions can diffuse the unfolding sectarian tragedy and reach a compromise on the presidency, another political crisis is sure to emerge, unless Lebanon's leaders – and its people – tackle the root causes of the country's instability. Eventually, the Lebanese will have to address the question of what kind of country they want: one built on sectarian gerrymandering or a more egalitarian way of sharing power.

• Mohamad Bazzi is the Edward R. Murrow Press Fellow at the Council on Foreign Relations in New York city.