The Syrian opposition was an umbrella term for the Syrian revolutionary organizations that opposed Bashar al-Assad's Ba'athist regime during the Syrian revolution and the Syrian civil war. The opposition factions in Syria became active as grassroots movements during the mass demonstrations against the Ba'athist regime. The Free Syrian Army (FSA) was the most prominent armed revolutionary group in the initial stages of the war; but it declined and became decentralized by 2015. By 2021, Hay'at Tahrir al-Sham (HTS) had become the strongest faction within the armed forces of the Syrian opposition.