|The Kurdish population of Syria is concentrated in the North|
The Syrian Kurds are Sunnis, just like the majority Arab population. The Kurds, however, are a totally distinct ethnic group, and constitute approximately 10% of the Syrian population. Like their Kurdish brethren in Iraq, Iran and Turkey, Syria's Kurds have long felt persecuted by the government in Damascus. Interestingly enough, the Assad regime has largely pulled out of Kurdish regions in Syria's north, leaving the country's two million Kurds with a degree of independence that was previously unimaginable. Why Assad did made this decision has been debated. Suggestions have run the gamut from his army simply being overstretched to his desire to tweak Turkey who worries about its' own restive Kurdish population seeing a largely independent Kurdish enclave right across their border in northern Syria.
The reality though is that for now, the Syrian Kurds are able to control their own destiny. As with Iraq's Kurds after the Gulf War, Syria's Kurds have moved quickly to expand their authority in Kurdish areas, and as this Washing Post article notes, have been just as quick to fight the largely Sunni Arab rebels as the Assad regime itself. The major issue dividing the Kurds and the Sunni rebels are what kind of government would come after Assad. The main Syrian opposition - the Free Syrian Army or FSA - is split between those who would look to some kind of democratic political system and others who demand an Islamic government based on Sharia, or Islamic Law.
The Kurds, by contrast, are not interested in any kind of Islamist political structure, and many Kurds are therefore leery of what a post-Assad, Sunni Arab dominated political system might look like. Furthermore, the Kurds in general are quite leery about being subject to Arab domination of any sort, especially now that they have tasted freedom. With two million people and an independent Kurdish fighting force, the Kurds are not eager to exchange the dictatorial rule of Assad with an Islamist government, and the Kurd-Sunni Arab fault line is yet one more demographic fault line within Syria.