What Next?

Iraq's neighbors are vulnerable to this aspect of spillover. Iraq's own divisions are mirrored throughout the region; for instance, Bahrain, Kuwait and Saudi Arabia all have sizable Shiite communities. In Saudi Arabia, Shiites make up about 10 percent of the population, but they are heavily concentrated in its oil-rich Eastern Province. Bahrain's population is majority Shiite, although the regime is Sunni. Likewise, Iran, Syria and Turkey all have important Kurdish minorities, which are geographically concentrated adjacent to Iraqi Kurdistan.

Populations in some countries around Iraq are already showing dangerous signs of radicalization. In March, after the Sunni jihadist bombing of the Shiite Askariya shrine in Iraq, more than 100,000 Bahraini Shiites took to the streets in anger. In 2004, when U.S. forces were battling Iraqi Sunni insurgents in Fallujah, large numbers of Bahraini Sunnis protested. There has been unrest in Iranian Kurdistan in the past year, prompting Iran to deploy troops to the border and even shell Kurdish positions in Iraq. The Turks, too, have deployed additional forces to the Iraqi border to prevent any movement of Kurdish forces between the two countries.

Most ominous of all, tensions are rising between Shiites and Sunnis in the key Eastern Province of Saudi Arabia. As in Bahrain, many Saudi Shiites saw the success of Iraq's Shiites and are now demanding better political and economic treatment. The government made a few initial concessions, but now the kingdom's Sunnis are openly accusing the Shiites of heresy. Religious leaders on both sides have begun to warn of a coming civil war or schism within Islam. The horrors of such a split are on display only miles away in Iraq.

Secession Breeds Secessionism

Iraq's neighbors are just as fractured as Iraq itself. Should Iraq fragment, voices for secession elsewhere will gain strength. The dynamic is clear: One oppressed group with a sense of national identity stakes a claim to independence and goes to war to achieve it. As long as that group isn't crushed immediately, others with similar goals can be inspired to do the same.

The various civil wars in the former Yugoslavia in the 1990s provide a good example. Slovenia was determined to declare independence, which led the Croats to follow suit. When the Serbs opposed Croatian secession from Yugoslavia by force, the first of the Yugoslav civil wars broke out. The European Union foolishly recognized both Slovene and Croatian independence, hoping that would end the bloodshed. However, many Bosnian Muslims wanted independence, and when they saw the Slovenes and Croats rewarded for their revolts, they pursued the same course. The new Bosnian government feared that if it did not declare independence, Serbia and Croatia would gobble up the respective Serb- and Croat-inhabited parts of their country. When Bosnia held a March 1992 referendum on independence, 98 percent voted in favor. The barricades went up all over Sarajevo the next day, kicking off the worst of the Balkan civil wars.

It didn't stop there. The eventual success of the Bosnians -- even after four years of war -- was an important element in the thinking of Kosovar Albanians when they agitated against the Serbian government in 1997-98. Serbian repression sparked an escalation toward independence that ended in the 1999 Kosovo War between NATO and Serbia. Kosovo, in turn, inspired Albanians in Macedonia to launch a guerrilla war against the Skopje government in hope of achieving the same or better.

In Iraq's case, the first candidate for secession is obvious: Kurdistan. If any group on Earth deserves its own country, it is surely the Kurds -- a distinct nation of 25 million people living in a geographically contiguous space with their own language and culture. However, if the Iraqi Kurds declare their independence and are protected by the international community, it is not hard to imagine Kurdish groups in Turkey and Iran following suit.

Moreover, the Kurds are not the only candidates. Shiite leader Abdul Aziz Hakim has called for autonomy for Iraq's Shiite regions -- a likely precursor for demands of outright independence. If Iraqi Shiites try to split off, other Shiites in the Gulf region might agitate against their own regimes along similar lines. Moreover, if ethnic or sectarian self-determination begins spreading throughout the Middle East more generally, secessionist movements could also spread to unlikely groups such as Iran's minority Azeri and Baluch populations.

Beware of Neighborly Interventions

Another critical problem of civil wars is the tendency of neighboring states to get involved, turning the conflicts into regional wars. Foreign governments may intervene overtly or covertly to "stabilize" the country in turmoil and stop the refugees pouring across their borders, as the Europeans did during the Yugoslav wars. Neighboring states will intervene to eliminate terrorist groups setting up shop in the midst of the civil war, as Israel did repeatedly in Lebanon. They also may intervene to stem the flow of "dangerous ideas" into their country. Iran and Tajikistan intervened in the Afghan civil war on behalf of co-religionists and co-ethnicists suffering at the hands of the rabidly Sunni, rabidly Pashtun Taliban, just as Syria intervened in Lebanon for fear that the conflict there was radicalizing its Sunni population.

In virtually every case, these interventions brought only further grief to the interveners and to the parties of the civil war.

Opportunism is another powerful motive. States often harbor designs on their neighbors' land and resources and see the chaos of civil war as an opportunity to achieve long-frustrated ambitions. Much as Croatia's Franjo Tudjman and Serbia's Slobodan Milosevic may have felt the need to intervene in the Bosnian civil war to protect their ethnic brothers, it seems clear that a more important motive for both was to carve up Bosnia between them.

Many states attempt to influence the course of a civil war by providing money, weapons and other support to one side. In effect, they use their intelligence services to create proxies who can fight the war for them. But states find that proxies are rarely able to secure their interests, typically leading them to escalate to open intervention. Both Israel and Syria employed proxies in Lebanon, for example, but found them inadequate, prompting their own invasions.