Iraq's insurgencies began with the U.S. military invasion in March 2003 and gained momentum after the fall of Saddam Hussein's regime when the United States moved to dissolve the Iraqi military and implement a sweeping de-Baathification policy. This convinced many Iraqis—particularly Sunni Arabs—that they were about to become victims rather than participants in the post-Saddam order. It drove them to join other disgruntled Iraqis in a fight to retain local power and destabilize the new central government.

Iraq has no shortage of weapons and people well trained in their use who are determined to wreak havoc on the occupiers and on Iraqis believed to support them. Porous borders, poor local security, and political disarray allow insurgents to act with impunity and to receive protection from frightened and angry kinsmen and sympathizers. Iraqi officials estimate the insurgents at five to fifteen thousand Iraqis, helped by several hundred foreign extremists with deadly skills and daring, and a potential support network of tens of thousands of Iraqis.

Insurgents fall into two basic categories: secular nationalists who want to return to the style of governance from which they benefited for more than eighty years, joined by "bitter-enders" with no particular vision for Iraq; and religious extremists who want to make Iraq into an Islamic state. All demand the immediate withdrawal of U.S. and other foreign forces and threaten Iraqis whom they perceive as collaborators or as insufficiently nationalist or Islamic. They have little else in common.

Nationalist-minded insurgents are mostly Saddam loyalists, former military men, members of tribes connected to Saddam, and hard-line Baathists. Their goals appear limited to regaining local power through a campaign of terror aimed at destabilizing Iraq and denying victory to the United States and successor Iraqi governments. Reportedly they receive support from Syrian Arab nationalists, remnants of the Iraqi Baath Party, and the extended tribal clans and confederations that sprawl across central and northwestern Iraq, Jordan, Saudi Arabia, and Syria. Many are probably linked as well to Sunni Arab Muslim extremists whose influence in Iraq appears to be spreading.

Iraq's religious insurgents are far more dangerous. They include Sunni and Shiite factions that emerged after the end of Saddam's rule from years underground or in exile. They share a vision of an Islamic Iraq where the Quran and Sharia are the only source of law, economic and social justice prevail (at least for Muslims), and all foreign influence has been removed. Arab Sunni extremist clerics have formed a political coalition, the Council of Muslim Scholars, and advocate attacks on U.S. forces. Fallujah and other towns in the Sunni heartland are under virtual Islamist rule, with women heavily veiled, men forced to wear beards, strict codes of Islamic law enforced, and harsh punishments meted out. Members of at least one faction, Ansar Al Sunna, trained in Afghanistan with Al Qaeda. Shiite insurgents are mainly those affiliated with Moqtada Al Sadr, the young leader from an important clerical family who expanded his father's support base in the Shiite shrine cities and created the Mahdi Army to attack foreign forces and moderate leaders. Sadr is supported primarily by young, urban, dispossessed and angry Iraqis. He is less popular among mainstream Shiites who look to the more moderate but aging Grand Ayatollah Ali Al Sistani for guidance.

Abu Musab Al Zarqawi is the most lethal of the extremist insurgents. Allegedly a Jordanian Islamic extremist who trained with Al Qaeda in Afghanistan, he claims responsibility for attacks against U.S. and other foreign targets, including the attack in August 2003 that killed the UN Secretary-General's Special Representative for Iraq Sergio Vieira de Mello. His loyalists appear to be most active in predominantly Sunni Arab areas of central and western Iraq. While Zarqawi's current relationship with Osama bin Ladin is not known, terrorism experts describe him more as a rival than as a follower of the Al Qaeda leader. Zarqawi's successes have spawned imitators among Iraq's indigenous insurgents.

Iraq's insurgents will continue to challenge U.S. forces and to test the endurance of post-Saddam governments. Insurgents in the Sunni Arab heartland probably will oppose the elections scheduled for January 2005 and use terrorism to keep fellow citizens from voting. Others, including nationalist insurgents, politicians displaced by the interim government of Prime Minister Iyad Allawi, and Sadr loyalists, may try to manipulate the electoral process to ensure the right people are elected to the new parliament and to the committee that will draft the permanent constitution. The insurgents are better organized and better armed than their moderate opponents. Allawi's efforts to negotiate with Sadr loyalists and urban and Sunni tribal leaders could defuse the more violent aspects of insurgent operations, but they will not end the attacks on U.S. forces and Iraqis seen to be collaborating with them. That will require cooperation from Iraqis in cities and towns throughout the country who have condoned insurgent activities and rejected reconciliation.

Judith S. Yaphe is Senior Fellow for the Middle East at the Institute for National Strategic Studies, National Defense University, Washington, DC. The opinions expressed here are hers and do not represent policies of the University, the Department of Defense, or any other government agency.