Across the Middle East, where Christianity was born and its followers once made up a sizable portion of the population, Christians are now tiny minorities. Driven by different factors  the search for better opportunities abroad, their status as targets of Iraq's sectarian conflict, a low birth rate, and discrimination  the trend largely holds true across a region where Christians have maintained a presence for two millenniums.

Where Are Christians Dwindling Most?

All around the region, Christians made up more than 20 percent of the population in the early 20th century; today, they make up less than 10 percent. Iraq has seen perhaps the most dramatic decline. Estimates of its Christian population at the time of the US-led invasion in 2003 ranged from 800,000 to 1.4 million, roughly 5 percent of the population. But targeted by killings, kidnappings, and threats, many fled  in far higher proportions than their Sunni and Shiite compatriots: an estimated 20 percent of Iraqi refugees abroad are Christians. Only an estimated 500,000 to 600,000 remain.

Why Are Their Numbers Dropping?

Outside Iraq, which is a unique case, the most common motivator is economics, not persecution. "People want to seek a better life, and that's relevant for all people in the region, Muslims as well," says Fiona McCallum, a professor at Scotland's University of St. Andrews who studies Christian communities in the Middle East. But Christians in the region have traditionally been better positioned to emigrate than their Muslim counterparts because of their higher education levels.

With a lower birth rate than Muslims, the Christian population would decline even without emigration as Muslim births outpace Christian births. And religious discrimination is also a factor. In Egypt, Coptic Christians say they are subject to systemic government discrimination. And in the Palestinian territories, Christians cite intimidation and land theft.

Is There More Tension With Muslims Now?

The level of sectarian strife in Iraq is certainly elevated. In Israel, relations between Muslims and Christians are generally stable, says Dr. Una McGahern, who recently completed her doctoral thesis on Palestinian Christians in Israel. "While there are elements within both communities who would view the other in more hostile terms, there is a broader consensus of unity and acceptance that exists and that builds on historic patterns of coexistence in the region," she says. In some cases, she adds, the two communities are brought together by perceived Israeli attempts to sow dissension.

Sectarian tensions have simmered in Egypt for decades, with periodic eruptions. Earlier this month, Muslims killed six worshipers leaving mass and a security guard  allegedly in revenge for a Christian's rape of a Muslim girl.

Hilal Khashan, professor of political studies at the American University in Beirut, says that tension has not increased, but that extra attention is given to violence against Christians, both in Egypt and Iraq. "Acts of violence that are driven by personal issues are frequent, but they only make the news when they involve Muslims against Copts," he says.

In Syria, where Christians have fallen to 10 percent, there are fewer tensions, however. President Bashar al-Assad, a member of a religious minority himself, has an interest in keeping sectarian strife at bay, and his regime rigidly cracks down on Islamic extremism. According to Dr. McCallum, many Syrian Christians feel they can participate in state and society, though they complain of discrimination in conversion and interreligious marriage.

Is the Rise of Political Islam a Factor?

In Egypt, where women once wore miniskirts on the street, most women are now veiled. It's one of many signs of the growing role that Islam plays in Egyptians' lives, which can leave Christians feeling uneasy. "You can't totally ignore that there has been a rise in political Islam & and obviously if you're not part of that you will feel a bit different," says McCallum. As Egypt's Christians watch the rise of Hamas in the Palestinian territories or Hezbollah in Lebanon, many are increasingly worried about their place in society.

What Effect Has the Exodus Had Regionally?

As Christians leave the Middle East, some worry they will leave behind an increasingly polarized society. When members of different religions or sects live side by side, they are more likely to see one another as people, rather than faceless adversaries, says McCallum. The loss of the Christians in the Palestinian territories and Israel, says McGahern, would be particularly tragic. "Diversity necessitates compromise and breeds creativity," she says. "Without Palestinian Christians or Druze or Muslims, or Jews for that matter, society would become more polarized and political options more rigid."