On Friday, the United Nations reported that nearly half of Syria's population has been displaced since the start of the civil war in 2011. Half. It's the equivalent of 135 million Americans being forced to move.

Three million Syrians have become refugees abroad and 6.5 million more have fled their homes for other locations within the country (a group known as "internally displaced people," or IDPs)—all told, roughly 43 percent of Syria's pre-war population of 22 million. The study comes a week after the UN announced that almost 200,000 people have died in the conflict. It's the "biggest humanitarian emergency of our era," according to the UN's refugee agency.

Relative to the advance of the Islamic State in Syria and Iraq, the war between Israel and Hamas, and the collapse of the Libyan government, the worsening humanitarian crisis in Syria has received scant attention in recent months. But it's no less consequential a development in the region. What does it mean for a country's future when half its people are uprooted? What does it mean for Syria's neighbors, including Lebanon, which now has the highest proportion of refugees of any country in the world, and Jordan, which has taken in a comparable number of Syrian refugees to all of Canada moving to the U.S.?