Syria is a multiple proxy war.
Between Sunni (Saudi & Qatar) and Shia (Iran)
Between America/UK/France and Russia.
Between Israel and Hezbollah/ Iran.
Between Jihadists/Salafists and moderate Islam.
Between Qatar and Russia for European gas supplies.
+probably more!
Plus the two big regional powers (Turkey and Israel) are flexing their muscles to show how important they are. And to choose the future shape of a neighbour country.
Plus the Kurds are trying to build a greater Kurdistan nation.
Then there is the co-operation between the security services of Russia, NATO and Israel to try and control extremist Islamic terrorists, chemical weapons and MANPADs.