Syria's civil war is nearly three years old now. It has claimed the lives of more than 120,000 people, forced 9 million to flee their homes, and caused a humanitarian crisis on a record scale. Earlier this week, the United Nations issued an appeal for $6.5 billion for Syrian aid -- its largest appeal ever for a single crisis. Fighting appears to be intensifying, especially in Aleppo, as both sides try to make gains before a scheduled peace conference in Switzerland on January 22. The situation on the ground remains incredibly complex and dangerous, with little real hope of immediate resolution. The photojournalists who shot the following photos did so at great personal risk; more than 20 journalists have been killed in the conflict so far, many more injured or abducted.