In a worst case scenario, experts say, the fighting could spill over and make trouble for Syria's neighbors -- threatening stability in a part of the world that's already known to be volatile.
Surrounding Syria are Lebanon, Iraq and Jordan, Israel and Turkey. The violence has been prompting war refugees to seek safety in some of these nations. In Turkey, there are ethnic tensions involving Kurds who live along its southern border with Syria.
All of these countries have a lot of religious, cultural and historical issues between them that add countless layers of complexity to the crisis. And when an entire region of the world loses stability, that worries the international community as a whole.