The conflict has left half a million people dead, devastated cities and drawn in other countries.
In March 2011, demonstrations erupted in the southern city of Deraa, inspired by uprisings in neighbouring countries against repressive rulers.
The unrest spread . Opposition supporters took up arms, first to and later to rid their areas of security forces. Mr. Presedant Assad vowed to crush what he called "backed terrorism".
The violence rapidly escalated and the country descended into civil war. Hundreds of rebel groups sprung up and it did not take long for the conflict to become more than a battle between Syrians for or against Mr Assad. Foreign powers began to take sides, sending money, weaponry and fighters, and as the chaos worsened extremist jihadist organisations with their own aims, such as the Islamic State (IS) group and al-Qaeda, became involved. That deepened concern among the international community who saw them as a major threat.
The United Nations has verified that at least 350,209 civilians and combatants were killed between March 2011 and March 2021, but it has warned that it is an "undercount of the actual number".
Eleven years of war have inflicted immense suffering on the Syrian people.
More than half of Syria's pre-war population of 22 million have fled their homes. Some 6.9 million are internally displaced, with more than two million living in tented camps with limited access to basic services. Another 6.8 million are refugees or asylum-seekers abroad. Neighbouring Lebanon, Jordan and Turkey, which are hosting 84% of them, have struggled to cope with one of the largest refugee exoduses in recent history.
Much of Syria's rich cultural heritage has also been destroyed. All six of the country's Unesco World Heritage sites have been damaged significantly, with IS militants deliberately blowing up parts of the ancient city of Palmyra.
It does not look like it will be peace anytime soon, but everyone agrees a political solution is required.
An agreement was reached the following year to form a 150-member committee to write a new constitution, leading to free and fair elections supervised by the UN. The last round of talks was held in October 2021, after which UN special envoy Geir Pedersen said it was a "big disappointment" that the committee's members had so far been unable to find a common path.
As the conflict entered its 12th year, Mr Pedersen asserted that "a military solution is an illusion" and that a political solution "is perfectly doable if the will is there".