Why is there a war in Syria?
A peaceful uprising against the president of Syria seven years ago turned into a full-scale civil war. The conflict has left more than 350,000 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 the "Arab Spring" in neighbouring countries.
When the 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.
How many people have died?
The Syrian Observatory for Human Rights a UK-based monitoring group with a network of sources on the ground, had documented the deaths of 364,371 people by August 2018, including 110,613 civilians.
The figure did not include 56,900 people who it said were missing and presumed dead. The group also estimated 100,000 deaths had not been documented.
Meanwhile, the Violations Documentation Center, which relies on activists inside Syria, has recorded what it considers violations of international humanitarian law and human rights law, including attacks on civilians.
It had documented 189,654 battle-related deaths, including 121,933 civilians, by June 2018.
What is the war about?
It is now more than a battle between those who are for or against Mr Assad.
Many groups and countries - each with their own agendas - are involved, making the situation far more complex and prolonging the fighting.
They have been accused of fostering hatred between Syria's religious groups, pitching the Sunni Muslim majority against the president's Shia Alawite sect.
Such divisions have led both sides to commit atrocities, torn communities apart and dimmed hopes of peace.
They have also allowed the jihadist groups Islamic State (IS) and al-Qaeda to flourish.
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.
The government's key supporters are Russia and Iran, while the US, Turkey and Saudi Arabia back the rebels.
Russia - which already had military bases in Syria - 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, France and other Western countries have provided varying degrees of support for what they consider "moderate" rebels.
A global coalition they lead has also carried out air strikes on IS militants in Syria since 2014 and helped an alliance of Kurdish and Arab militias called the Syrian Democratic Forces (SDF) capture territory from the jihadists.
Turkey has long supported the rebels but it has focused on using them to contain the Kurdish militia that dominates the SDF, accusing it of being an extension of a banned Kurdish rebel group in Turkey.
Saudi Arabia, which is keen to counter Iranian influence, has also armed and financed the rebels.
Israel, meanwhile, has been so concerned by what it calls Iran's "military entrenchment" in Syria and shipments of Iranian weapons to Hezbollah that it has conducted hundreds of air strikes in an attempt to thwart them.
How has the country been affected?
As well as causing hundreds of thousands of deaths, the war has left 1.5 million people with permanent disabilities, including 86,000 who have lost limbs.
At least 6.6 million Syrians are internally displaced, while another 5.6 million have fled abroad.
Neighbouring Lebanon, Jordan and Turkey, where 93% of them now live, have struggled to cope with one of the largest refugee exoduses in recent history.
By the end of May 2018, some 13 million people were estimated to be in need of humanitarian assistance, including 5.2 million in acute need.
The warring parties have made the problems worse by refusing aid agencies access to many of those in need. Almost 1.5 million people were living in besieged or hard-to-reach areas as of July 2018.
Syrians also have limited access to healthcare.
Physicians for Human Rights had documented 492 attacks on 330 medical facilities by the end of December 2017, resulting in the deaths of 847 medical personnel.
Much of Syria's rich cultural heritage has also been destroyed. All six of the country's six Unesco World Heritage sites have been damaged significantly.
Entire neighbourhoods have been levelled across the country.
Interactive See how Jobar, Eastern Ghouta, has been destroyed
In one district in the Eastern Ghouta - a former rebel bastion outside Damascus - 93% of buildings had been damaged or destroyed by December 2017, according to UN satellite imagery analysis. The government's six-week ground offensive that began in February 2018 caused further destruction.
How is the country divided?
The government has regained control of Syria's biggest cities but large parts of the country are still held by rebel and jihadist groups and the Kurdish-led SDF alliance.
The last remaining opposition stronghold is the north-western province of Idlib.
Despite being designated a "de-escalation zone", troops are massing nearby for an expected offensive. The government says it wants to "liberate" Idlib from jihadists linked to al-Qaeda.
But the UN has warned of a "bloodbath" if there is an all-out assault on the province, which is home to some 2.9 million people, including a million children.
Hundreds of thousands of civilians are already experiencing dire conditions in overcrowded sites in which basic services have been stretched to breaking point for months.
The SDF meanwhile controls most territory east of the River Euphrates, including the city of Raqqa. Until 2017, it was the de facto capital of the "caliphate" proclaimed by IS, which now controls only a few pockets of land across Syria.
Will the war ever end?
It does not look like it will anytime soon, but everyone agrees a political solution is required.
But nine rounds of UN-mediated peace talks - known as the Geneva II process - since 2014 have shown little progress.
President Assad appears unwilling to negotiate with the opposition. The rebels still insist he must step down as part of any settlement.
Meanwhile, Western powers have accused Russia of undermining the peace talks by setting up a parallel political process.
The so-called Astana process saw Russia host a "Congress of National Dialogue" in January 2018. However, most opposition representatives refused to attend.