U.S. Policy on Syria: Why America is powerless in Syria

On the Ides of March, the Syrian civil war began its eighth year of fighting. The original war, between the Bashar al-Assad regime and Sunni Arab rebels, is largely over. Additionally, the American-led fight against the Islamic State is ending. However, these two facts do not equal an end to the fighting nor to the immense suffering that Syrian citizens continue to endure. Why is it proving so difficult to stop the hostilities? Why are efforts by global leaders, including the U.S., unable to push the warring parties towards a peaceful settlement? Perhaps it is because the global leaders themselves have new objectives in the region. If this is the case, what is current U.S. policy toward the war-torn region?