In recent news, Russia is pulling the bulk of it’s troops from Syria for multiple reasons.
1. The economy of Russia has been in a weak state since the price of oil has dropped, which is what the Russian economy is directly linked to. So, waging a war inside of Syria is costly. Plus, this keeps them from investing more into Syria if something was to happen. The Russians not wanting another war like the Soviet invasion of Afghanistan.
2. Mission objects were reportedly completed, with over nine thousand airstrikes, and 400 populated local areas freed from ISIS/Al Nusra/Rebel control. These five months gave the Syrian Government time to recuperate their war torn forces, all while putting mounting pressure on rebel/terrorist groups operating in Syria.
3. The peace talks will start soon, and according to the Kremlin, a withdraw of troops will help the talks go smoother, which this is true. Russia has also shown when things don’t go their way, they will be more than happy to use military force, which is why there will be troops still on the ground in a minimal role, most likely Special forces and military contractors. Russia has also stated it will keep some air-power there. This could also be seen as a deterrent to Turkish and Saudi military operations in Syria, which both Saudi Arabia and Turkey have stated they are more than ready to conduct operations.
While terrorism in Syria will probably not be quelled for awhile. Russian, French, and US/Coalition airstrikes have beaten back ISIS to a shell of it’s former capacity to fight. ISIS will not be stopped unless someone is willing to invest a lot of money, time, and troops into the region. That is the only way, ISIS will be destroyed.