Bashar al Assad's allies help prop up the regime. In many battles they have changed the course of the war.
The Syrian regime has retaken most of the rebel-held parts of eastern Aleppo following years of fighting. But the recapture of Syria's once biggest city may not have been possible without the backing Assad's forces got from its allies, Russia, Iran, and Hezbollah.
Hezbollah is a Shia militant group. It is a key non-state actor backing the Syrian regime in its fight against opposition groups. Up to 4,000 Hezbollah fighters have been fighting alongside regime forces since 2013. Ten of its senior leaders have been killed in the struggle for Syria.
A second major ally of the Syrian regime is Iran which is providing Assad's forces with military advice, arms, and funding. The head of Iran's elite Quds forces, Qasem Soleimani, is the commander of the regime's Shia militias.
Russia came to the aid of the Syrian regime in September 2015, saying it would target only Daesh. But Russian air strikes have also hit opposition groups and opposition-held areas.
The course of the war in Syria might have been different had the Assad regime not had the backing of these forces.