It’s remarkable how quickly everyone remembered the patterns set during Lebanon’s long civil war. When violence suddenly erupted in Beirut on the afternoon of January 25, people rushed to stock up at grocery stores, businesses quickly shut their doors and traffic was snarled throughout the city as everyone hurried home.

While most people prepared for a siege, others were intent on causing trouble: Bands of young vigilantes roamed the streets, armed with wooden clubs and metal pipes, eyeing passing cars for any strangers. The fighting started in the cafeteria of Beirut Arab University between Shiite and Sunni students. In less than an hour, it spread to the surrounding neighborhood of Tariq Al-Jadideh, a Sunni stronghold. Snipers took up positions on the roofs of residential buildings, firing at protesters and Lebanese soldiers trying to break up the melee. Bands of Sunnis and Shiites–some wearing blue and red construction helmets–fought running street battles with rocks and clubs. Armed men roamed through the crowds. Rioters set fire to cars and trash dumpsters, sending plumes of black smoke over the neighborhood.

By the time it was over, four people were killed, more than 150 were injured and the Lebanese army had imposed a curfew on Beirut for the first time since 1996. Rumors circulated wildly, evoking memories of the civil war. The most disturbing news was broadcast on Lebanese television stations shortly before the curfew: Armed vigilantes had set up a checkpoint on the highway linking south Lebanon to Beirut. They were asking people for their 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 fifteen-year civil war. One of the war’s earliest massacres took place in December 1975, during the so-called “Black Saturday,” when gunmen from the right-wing Christian Phalange militia set up checkpoints throughout Beirut and killed dozens of Muslims. That a checkpoint was erected within the short hours of violence on January 25 illustrates how close Lebanon might be to the brink of another civil war.

In the last war, the sectarian divide was between Muslims and Christians. This time the conflict is mainly between Sunnis and Shiites. It’s also an extension of the ongoing proxy war in Iraq–pitting Iran against an alliance of the United States, Saudi Arabia and other Arab regimes.

There is one major, underreported reason for Lebanon’s slide toward civil war: blowback from Iraq. Fearing the sectarian bloodbath in Iraq and Iran’s growing regional influence, Lebanese Sunnis feel besieged as never before, and they’re lashing out at Shiites. As they confronted Hezbollah supporters during a nationwide strike last week, some groups of Sunnis waved posters of Saddam Hussein. It was a rich contradiction: US-allied Sunnis carrying posters of Saddam, a dictator the United States spent billions of dollars and lost thousands of lives to unseat. But it was also a declaration of war: Saddam, after all, killed hundreds of thousands of Shiites in Iraq. Many Lebanese Shiites have relatives in Iraq, and the two communities have had close ties for decades.

Two days before the rioting at Beirut Arab University, I stood on a street corner in a mixed Beirut neighborhood with a group of about 100 Sunni men clutching wooden clubs and metal chains. Many of them were wearing blue headbands, the color of the US- and Saudi-backed Future Movement, led by Saad Hariri, son of former Prime Minister Rafik Hariri, who was assassinated in February 2005. They were stopping the few cars coming into the area, looking for “strangers”–a code word for Shiites.

“This area is 100 percent Sunni,” says Maher Amneh, a 32-year-old clothing-store owner wearing a wool cap and carrying a metal pipe. “We all know each other. So if we see anyone strange, it means he doesn’t belong here.”

“So there are no Shiites in this area?” I ask him.

“No. And everyone knows that,” he replies. (We happened to be standing opposite one of the city’s best Lebanese restaurants, a hole-in-the-wall place called Abu Hassan. It’s owned by a Shiite from the south.)

“So what would you do if you saw a stranger?”

“We would ask him, ‘What are you doing here, now, at this time?'” he says nonchalantly. “And if he doesn’t give us an answer, it means he’s coming from them [Hezbollah], and he wants to take a look–to count us.”

That day, January 23, Hezbollah and its allies had organized a nationwide strike as part of their campaign to topple the US-backed Lebanese government. Before dawn, the Party of God dispatched groups of young Shiite men, some wearing ski masks, to close roads by burning tires and cars. Hezbollah’s Christian allies, especially the Free Patriotic Movement led by Maronite politician and former army commander Michel Aoun, also took to the streets in Christian areas. Three people were killed and dozens wounded in clashes throughout the country before the strike was called off that night.

As soon as Hezbollah bused its supporters into Sunni areas of Beirut to close roads and force people to stay home, local Sunnis took to the streets. They saw it as an invasion by Hezbollah. At the intersection where I met Maher, two men from the Future Movement sat in a black SUV, talking into walkie-talkies and earpieces and directing their men. About 500 yards away a group of Hezbollah supporters had closed Beirut’s seaside corniche and milled around a burned car in the middle of the street. They too had men with walkie-talkies directing them.

“The Shiites are occupying our area,” says Bahi Amneh, a 19-year-old finance student and Maher’s cousin. “It’s our duty to free it. They came here from the southern suburbs to force everyone into a strike. It’s our duty to make them leave. If they don’t, we will attack them.”

“Why are Shiites the only ones allowed to have weapons?” one of his friends interjects. “Why aren’t Sunnis allowed?”

As Bahi and his friends gathered around the men in the black SUV with tinted windows, more people began joining in. Young men came around the corner on mopeds.

“You know, it’s just unfair. We want to live in peace. But every time we try, Hezbollah makes trouble,” Bahi says bitterly. “Hezbollah has its own country within Lebanon. They have weapons. They don’t respect the laws.” A few minutes later shots rang out, and the two groups began throwing chunks of cinder blocks at each other as Lebanese soldiers rushed to separate them.

How did things deteriorate to this point, where Lebanese Sunnis and Shiites are increasingly afraid of each other? At the end of the civil war in 1990, all militias were disarmed under the Saudi-brokered Taif Accord. But Hezbollah was allowed to keep its weapons as a “national resistance” against the Israeli occupation of south Lebanon, which ended in 2000. After the 2005 assassination of Rafik Hariri–Lebanon’s most prominent Sunni leader–international pressure and mass demonstrations forced Syria to withdraw its troops from Lebanon. The Bush Administration then began pressuring the government of Prime Minister Fouad Siniora, which took office after elections in June 2005, to disarm Hezbollah.

The current crisis erupted last July, when Hezbollah abducted two Israeli soldiers in a cross-border raid. That set off a thirty-four-day war with Israel. After the war, Hezbollah began accusing Siniora’s government of being a US puppet and demanded more seats in the twenty-four-member Cabinet. When talks to form a national unity government failed in November, six ministers representing Hezbollah and its allies resigned from the Cabinet. Siniora’s ruling coalition–of Sunni, Christian and Druse parties–accuses Hezbollah of walking out of the government to block a United Nations investigation into Hariri’s murder, which has been widely blamed on Syria.

Hezbollah’s leader, Sayyid Hassan Nasrallah, has repeatedly vowed that his group will never use its weapons against fellow Lebanese. But Sunnis are worried that, left unchecked, the militia will be tempted to take power by force.

After Hezbollah and its allies began an open-ended protest in downtown Beirut on December 1, setting up hundreds of tents outside the main government palace, relations between Sunnis and Shiites deteriorated quickly. All the while, Lebanese Sunnis were keeping a wary eye on developments in Iraq, where Shiite death squads were killing Sunnis and Iran was extending its influence over the Iraqi government.

Then came Saddam’s execution on December 30. Many Sunnis view the United States and the Shiite-dominated Iraqi government as killing off the last vestiges of Arab nationalism by executing Hussein. He was among the few Arab leaders who defied the West. In the Sunni view, America and its allies eradicated the idea of a glorious Arab past without offering any replacement for it, other than sectarianism. And the repercussions are being felt in Lebanon.

“The Saddam execution and Hezbollah’s drive for political power are making Sunnis very nervous about Shiite actions,” says Amal Saad-Ghorayeb, author of Hizbullah: Politics and Religion and a visiting scholar at the Carnegie Middle East Center in Beirut. “Sunnis support Hezbollah wholeheartedly when it comes to resistance against Israel. But when it comes to political power, that changes the equation, and Hezbollah is seen as a threat when it directs its power inside Lebanon.”

Because Shiites are a plurality in Lebanon–making up about 40 percent of a total population of 4 million–and because they are more powerful militarily and politically than in many other countries, Sunni-Shiite tensions are more pronounced in Lebanon.

After last summer’s war, members of Siniora’s ruling coalition quickly demanded that Hezbollah disarm, as required by the UN cease-fire resolution. Many Shiites, who viewed Hezbollah as their protector during the war, felt threatened by these demands, which drove them even closer to the militia.

“This was a sect whose houses and farms had been destroyed, who lost their livelihoods, but they had not been humiliated because of the way Hezbollah fought,” says Wassif Awada, a columnist at the Beirut daily as-Safir. “Then some government leaders started demanding that Hezbollah give up its weapons, without leaving any time for the wounds to heal. Many Shiites felt like their identity was under attack after the war. They became more attached to Hezbollah because they view this as a battle for their existence.”

Arab regimes and the United States are rushing to shore up Siniora’s government. On January 25, the same day of the bloody protests and curfew in Beirut, Siniora attended a donors conference in Paris, where he received pledges of $7.6 billion in aid and loan guarantees. Some of the funding will go toward reconstruction after last summer’s war, but much of it will be used to make interest payments and refinance Lebanon’s crushing $41 billion public debt. The country’s debt-to-GDP ratio is now about 180 percent–the second-highest in the world (after Malawi). A large proportion of the pledges received at the Paris III conference are tied to unpopular economic reforms that Siniora has vowed to undertake, including raising taxes and privatizing state assets. Most of these measures–such as raising gasoline surcharges and the value-added tax–will most heavily affect Lebanon’s poor and working classes, who are disproportionately Shiite.

Saudi Arabia led the list of donors, promising $1.1 billion in credits and grants. It was followed by the United States, which pledged $770 million, pending Congressional approval. Coupled with $230 million pledged after the summer war, US aid could top $1 billion–more than Washington has ever given Lebanon in the past. Before Siniora took office in 2005, US aid to Lebanon had hovered around $40 million a year.

The Bush Administration is allocating $220 million to provide training and equipment–including small arms, ammunition and Humvees–to the Lebanese Army. In past years, US funding for Lebanese Army and security forces had hovered around $2-3 million per year.

Most troubling to Shiites is that the United States has set aside another $60 million to fund the Internal Security Force, a branch whose size has been nearly doubled to 24,000 troops by Siniora’s government since it came to power. The ISF has been filled with several thousand Sunni recruits, raising concerns among Shiites that it is intended as a counterweight to Hezbollah. The ISF–which answers to the Hariri-controlled Interior Ministry–was recently armed with weapons and equipment from the United Arab Emirates, a US ally that is worried about Iran’s regional role. Siniora has also created a new intelligence branch–reportedly dominated by Sunnis and Christians–and expanded a special commando unit known as the Panthers.

This funding is being perceived as a US effort to arm Sunnis against Shiites. In recent weeks, Hezbollah’s TV station, Al Manar, has frequently aired footage of US military planes at Beirut airport. The announcer asks, in an ominous tone, “What are these planes doing in Beirut?” He then notes that airport and government officials refused to comment.

“The ISF has been filled with Hariri’s people. It has become a militia of sorts,” says Saad-Ghorayeb. “It’s dangerous for the US to be seen as arming one faction against another.” In the volatile sectarian climate that pervades Lebanon today, perception is as dangerous as reality.