This kind of aid has undoubtedly helped make refugee flows more manageable for neighboring governments -- particularly in a place like Jordan, a politically fragile and by no means prosperous country that's already home to 480,000 Syrians. But in the first half of 2013, the refugee crisis (and the war in general) accelerated at a rate that few had really anticipated , and there's a real possibility that, barring a resolution to the conflict, Syria's neighbors will simply become too overburdened --or too worried about internal stability -- to take in additional refugees. After Kerry's speech, two of the world's leading officials dealing with refugee affairs gave me the sense that decision-makers are anticipating a significantly worsening crisis. And they're acutely aware of a nightmeric possibility from a humanitarian standpoint: the potential that Syria's neighbors, overwhelmed with refugees and threatened with spillover violence, will simply seal their borders.

Alexander Aleinikoff, the U.N.'s Deputy High Commissioner for Refugees, says that his agency's planning figures assume that there will be 3 million refugees living outside of Syria by the end of 2013, along with 6 million internally displaced -- if this happens, one out of every four people in Lebanon will be a Syrian refugee a little over six months from now. There are no refugee camps in Lebanon, a cycically unstable country where over 550,000 Syrians compete with locals for jobs and resources; inside of Jordan, only between a quarter and 40 percent of Syrian refugees actually live in camps.

Aleinikoff says that it's "absolutely...viewed as a possibility" that neighboring countries could tighten border controls based on any number of factors. "If the numbers [of refugee arrivals] continue at this level or grow, if the war spreads across borders, if the fight in Syria now begins to be seen as a substantial security risk in the bordering countries....I would expect to see the borders if not closed, than much more closely managed," he says.

This has already started to happen, to an extent: Aleinikoff says that there are "tens of thousands" of Syrians living along the Turkish border, waiting to be admitted into the country's northern neighbor. This situation in Iraq is even more troubling. "The Iraq border has been closed in parts for people trying to flee into Iraq," says Aleinikoff.

Anne Richard, the Assistant U.S. Secretary of State for Population, Refugees and Migration, confirmed this. "At one point the Iraqis were letting people across for medical care but they weren't allowing men of fighting age," she said.

Iraq has taken in over 150,000 Syrian refugees, a substantial number by any standard. But their reported stinginess along the border isn't surprising, and is an example of how humanitarian concerns might dovetail with political ones: Iraq has a mostly-Shi'ite leadership that has given overflight rights to Iranian aircraft resupplying the Assad regime. Meanwhile, Iraq's minorities have chafed against the increasingly unitary rule of Prime Minister Nouri Al Maliki, leading to a rash of terror attacks in the country's Sunni heartland, and tension with the Kurdish north over a proposed oil pipeline with Turkey.