If you want to understand the wider repercussions of the war between Hezbollah and Israel, buy a brilliant and very readable new book called “The Shia Revival: How Conflicts Within Islam Will Shape the Future.”

The author, Vali Nasr, is a professor at the Naval Postgraduate School in Monterey, Calif., and a top expert on Shiite Islam and the historic conflict between Shiite and Sunni Muslims. He just briefed President Bush on internal Iraqi religious and political dynamics. One can only wish the meeting had come three years sooner.

The United States is now caught in the middle of the Shiite-Sunni conflict in Baghdad, and the Lebanon war has worsened the precarious U.S. position. This sectarian struggle will determine the outcome of America’s Iraq venture. Nasr believes it will shape the future of the entire Middle East.

Shiite concentration

Shiites make up only 10 to 15 percent of the world’s 1.3 billion Muslims. U.S. Mideast policy has traditionally been focused on Sunni countries led by Arab allies in Egypt, Saudi Arabia and Jordan. But as Nasr points out: “In the Islamic heartland from Lebanon to Pakistan there are roughly as many Shias as there are Sunnis,” and around the geopolitically sensitive Persian Gulf, Shiites constitute 89 percent of the population.

Nasr gives a fascinating short course on the historic differences between Shiites and Sunnis, which stem from a dispute about who were the rightful heirs to the Prophet Muhammad. The Shiites believe his direct descendants should have inherited the mantle, starting with his cousin and son-in-law Ali. Sunnis endorsed the Prophet’s companions and slaughtered Ali’s son, Hussayn, whose death precipitated a historic Shiite embrace of martyrs. But the differences go deeper, to the essence of theology. Sunnis emphasized order and coming to terms with secular rulers. Shiites are searching for justice and look to clerics rather than caliphs or kings for guidance.

Prior to 1993, the only country ruled by Shiites was Persian Iran. Shiites were marginalized and persecuted in the Sunni Arab world and disdained by Sunni fundamentalists as apostates. Then came the war in Iraq, which altered the power balance in the Middle East.

When the United States toppled Saddam Hussein, it upended a regime whose Sunni leaders repressed a predominately Shiite population. U.S. leaders thought Iraq was dominated by a secular middle class. They believed an Iraqi democracy led by elected Shiite officials would encourage Iranian Shiites to overthrow their regime.

Hard reality

Reality bit hard. Iraq’s Shiite majority was predominantly religious. Shiite political leaders, who had spent their exile years in Tehran, would not drop their ties with the Iranians.

By removing Saddam, the United States made Shiite Iran the strongest power in the region. Urged on by their ayatollahs, Iraq’s Shiite majority voted in the second Shiite-led government in the region, dominated by religious parties. This Shiite revival helped other minority Shiite movements in the region, such as Lebanon’s Hezbollah, strengthen their position. They were aided by Iran, and – in Hezbollah’s case – by elections.

Nasr believes this Shiite ascendancy need not have been a negative for the region. Iraq’s preeminent Shiite cleric, Ayatollah Ali al-Sistani, is a moderate who accepts the idea of inclusive, constitutional government (with a strong role for clerics in the background). Such a religious/constitutional model could have set a new trend.

U.S. missteps

But U.S. missteps in Iraq opened the door to a virulent Sunni insurgency that deliberately targeted Shiite civilians. The late Abu Musab al-Zarqawi and his al-Qaida followers in Iraq wanted a civil war and used hatred of Shiites to recruit Sunni Arab jihadis.

Iraq’s Shiites have grown increasingly impatient with the inability of the United States to curb Sunni attacks on their civilians. Many Shiites suspect that the United States, nervous about Iranian influence, is turning against them and moving back toward its traditional support of Arab Sunnis.

Sistani’s calls to refrain from revenge are heeded less and less by his followers; the Shiite militia led by radical Shiite cleric Muqtada al-Sadr has murdered innumerable Sunni civilians, and is growing in strength.

Enter the war in Lebanon.

Iraqi Shiites, Nasr told me, have close ties to their co-religionists in Lebanon and are shocked by the U.S. support for Israeli bombing of Shiite areas. “Now Iraqis see the United States as anti-Shia in Lebanon,” Nasr says. “We are close to losing the Shia in Iraq.”

Iraqi Shiites worried

He worries that Iraqi Shiites will believe that the United States has turned its back on them and will now turn to Hezbollah’s Sheikh Hassan Nasrallah as their model rather than the moderate Sistani. If this happens, Shiite militias will soon start attacking U.S. troops, which would make a U.S. exit from Iraq almost inevitable.

After that exit, a Shiite-Sunni civil war would explode into full flower in Iraq, threatening Sunni regimes in the region and driving oil prices beyond the stratosphere.

Nasr argues that the United States would have been (and still would be) smarter to engage with Iran over Iraq and Lebanon. That means putting our demands on the table but being cognizant of theirs. “This might create a certain stability that allows you to contain some of these trends,” he says. “The moment of opportunity,” he adds, “is fast closing.”