Why has the Syrian war lasted 12 years?
A peaceful uprising against the president of Syria 12 years ago turned into a full-scale civil war. The conflict has left half a million people dead, devastated cities and drawn in other countries.
How did the Syrian war start?
Even before the conflict began, many Syrians were complaining about high unemployment, corruption and a lack of political freedom under President Bashar al-Assad, who succeeded his father, Hafez, after he died in 2000.
In March 2011, pro-democracy demonstrations erupted in the southern city of Deraa, inspired by uprisings in neighbouring countries against repressive rulers.
When the Syrian government used deadly force to crush the dissent, protests demanding the president's resignation erupted nationwide.
The unrest spread and the crackdown intensified. Opposition supporters took up arms, first to defend themselves and later to rid their areas of security forces. Mr Assad vowed to crush what he called "foreign-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.
Syria's Kurds, who want the right of self-government but have not fought Mr Assad's forces, have added another dimension to the conflict.
How many people have died?
The United Nations Human Rights Office estimated last year that 306,887 civilians - 1.5% of the total pre-war population - were killed between March 2011 and March 2021 due to the conflict.
It said 143,350 civilian deaths were individually documented by various sources with detailed information, and that a further 163,537 deaths were estimated to have occurred using statistical techniques. At least 27,126 of those estimated to have been killed were children.
The then-UN Commissioner for Human Rights, Michelle Bachelet, stressed that the fatalities were the "direct result of war operations", adding: "This does not include the many, many more civilians who died due to the loss of access to healthcare, to food, to clean water and other essential human rights."
The Syrian Observatory for Human Rights (SOHR), a UK-based monitoring group with a network of sources on the ground, had documented the deaths of 503,064 people by March 2023. It said at least 162,390 civilians had been killed, with the Syrian government and its allies responsible for 139,609 of those deaths.
The group estimated that the actual toll from the war was more than 613,400, with an additional 55,000 civilians believed to have died of torture in government-run prisons.
Another monitoring group, the Violations Documentation Center, which relies on information from activists across the country, had documented 240,215 battle-related deaths, including 145,765 civilians, as of March 2023.
The government's key supporters have been Russia and Iran, while Turkey, Western powers and several Gulf Arab states have backed the opposition to varying degrees during the conflict.
Russia - which had military bases in Syria before the war - launched an air campaign in support of Mr Assad in 2015 that has been crucial in turning the tide of the war in the government's favour.
The Russian military says its strikes only target "terrorists" but activists say they regularly kill mainstream rebels and civilians.
Iran is believed to have deployed hundreds of troops and spent billions of dollars to help Mr Assad.
Thousands of Shia Muslim militiamen armed, trained and financed by Iran - mostly from Lebanon's Hezbollah movement, but also Iraq, Afghanistan and Yemen - have also fought alongside the Syrian army.
The US, UK and France initially armed what they considered "moderate" rebel groups. But they have prioritised non-lethal assistance since jihadists became the dominant force in the armed opposition.
A US-led global coalition has also carried out air strikes and deployed special forces in Syria since 2014 to help an alliance of Kurdish and Arab militias called the Syrian Democratic Forces (SDF) capture territory once held by IS militants in the north-east and stop the jihadist group rebuilding.
Turkey is a major supporter of the opposition, but its focus has been on using rebel factions to contain the Kurdish YPG militia that dominates the SDF, accusing it of being an extension of a banned Kurdish rebel group in Turkey.
Turkish troops and allied rebels have seized stretches of territory along Syria's northern border and intervened to stop an all-out assault by government forces on the last opposition stronghold of Idlib.
Saudi Arabia, which is keen to counter Iranian influence, armed and financed the rebels at the start of the war. Having refused to engage with President Assad for more than a decade, it is now discussing how to facilitate Syria's "return to the Arab fold".
Israel, meanwhile, has been so concerned by what it calls Iran's "military entrenchment" in Syria and shipments of Iranian weapons to Hezbollah and other Shia militias that it has conducted air strikes with increasing frequency in an attempt to thwart them.
How has the country been affected?
Twelve years of war have inflicted immense suffering on the Syrian people.
In addition to the bloodshed, more than half of Syria's pre-war population of 22 million have had to flee their homes. Some 6.8 million are internally displaced, with more than two million living in tented camps with limited access to basic services.
Another 6 million are refugees or asylum-seekers abroad. Neighbouring Lebanon, Jordan and Turkey, which are hosting 5.3 million of them, have struggled to cope with one of the largest refugee exoduses in recent history.
At the start of 2023, the UN said 15.3 million people inside Syria were in need of some form of humanitarian assistance - an all-time high since the war began - and 12 million did not know where their next meal was coming from.
The already dire humanitarian situation in north-western Syria - the location of the last opposition stronghold - was made significantly worse by the huge earthquake that struck near the Turkish city of Gaziantep, about 80km (50 miles) from the Syrian border, on 6 February 2023.
More than 5,900 people were killed across Syria and another 8.8 million were affected, according to the UN. Thousands of homes and critical infrastructure were destroyed, leaving many families without food, water and shelter. Deliveries of life-saving aid to opposition-held areas were also delayed for days because of what a UN panel described as "shocking" failures by the warring parties as well as the international community.
The disaster happened at a time when the prices of food and fuel in Syria were already skyrocketing because of runaway inflation and the collapse of its currency, as well as the global crisis exacerbated by the war in Ukraine.
Syria has also been one of the countries in the Middle East worst affected by the Covid-19 pandemic - although the true extent is not known because of limited testing - and is now also having to deal with a deadly cholera outbreak that was made worse by the earthquake.
Access to medical care is severely restricted for the sick and injured because only half of the country's hospitals are fully functional.
Despite their protected status, 601 attacks on at least 400 separate medical facilities had been documented by Physicians for Human Rights as of February 2022, resulting in the deaths of 942 medical personnel. The vast majority of the attacks were blamed on government and Russian forces.
Entire neighbourhoods and vital infrastructure across the country also remain in ruins. UN satellite analysis suggested that more than 35,000 structures were damaged or destroyed in Aleppo city alone before it was recaptured by the government in late 2016.
Much of Syria's rich cultural heritage has likewise 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.
A UN commission of inquiry has concluded that the warring parties "have cumulatively committed almost every crime against humanity... and nearly every war crime applicable in a non-international armed conflict".
"Syrians," a February 2021 report says, "have suffered vast aerial bombardments of densely populated areas; they have endured chemical weapons attacks and modern day sieges in which perpetrators deliberately starved the population along medieval scripts and indefensible and shameful restrictions on humanitarian aid".
Who is in control of the country now?
The government has regained control of Syria's biggest cities, but large parts of the country are still held by rebels, jihadists and the Kurdish-led SDF. There have been no shifts in the front lines for three years.
The last remaining opposition stronghold is in the north-western province of Idlib and adjoining parts of northern Hama and western Aleppo provinces.
The region is dominated by a jihadist alliance called Hayat Tahrir al-Sham (HTS), but is also home to mainstream rebel factions backed by Turkey. An estimated 2.9 million displaced people, including a million children, are living there, many of them in dire conditions in camps.
In March 2020, Russia and Turkey brokered a ceasefire to halt a push by the government to retake Idlib. That led to an extended lull in violence, but there continues to be sporadic clashes, air strikes and shelling.
In the country's north-east, Turkish forces and allied Syrian rebels launched an offensive against the SDF in October 2019 to create a "safe zone" clear of Kurdish YPG militia along the Syrian side of the border, and have occupied a 120km (75 miles) long stretch since.
To halt the assault the SDF struck a deal with the Syrian government that saw the Syrian army return to the Kurdish-administered region for the first time in seven years. Despite the presence of Syrian troops, there are still regular clashes between the SDF and Turkish-led forces along the front line.
IS sleeper cells also continue to carry out frequent and deadly attacks.
Will the war ever end?
It does not look like it will anytime soon, but everyone agrees a political solution is required.
The UN Security Council has called for the implementation of the 2012 Geneva Communiqué, which envisages a transitional governing body "formed on the basis of mutual consent".
Nine rounds of UN-mediated peace talks - known as the Geneva II process - failed to make progress, with President Assad apparently unwilling to negotiate with political opposition groups that insist he must step down as part of any settlement.
Russia, Iran and Turkey set up parallel political talks known as the Astana process in 2017.
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. But little progress has been achieved after eight rounds of talks.
As the conflict entered its 13th year, UN special envoy Geir Pedersen said the situation in Syria was "untenable" and that "to carry on in the same manner, defies humanity and logic".
But he also expressed hope that the devastating earthquake could be a "turning point", noting the "humanitarian steps from all sides that have moved beyond previous positions, even if temporarily".