Rebel groups in Syria are battling regime forces as they push towards the capital, Damascus, posing a direct challenge to President Bashar al-Assad's power. The advances by opposition groups have changed the landscape of the civil war and raised fears of chaos if the government loses control. The conflict, which began in 2011, involves domestic opposition groups, extremist factions, and international powers such as the US, Iran, and Russia. The rebels have seized much of Syria's northwest, including the major city of Aleppo, and are now threatening the strategic city of Homs and edging closer to Damascus.