What began as a peaceful uprising against Syria's President Bashar al-Assad six years ago became a full-scale civil war that has left more than 300,000 people dead, devastated the country and drawn in global powers.
How did the war begin?
Long before the conflict began, many Syrians complained about high unemployment, widespread corruption, a lack of political freedom and state repression under President Bashar al-Assad, who succeeded his father, Hafez, in 2000.
In March 2011, pro-democracy demonstrations inspired by the Arab Spring erupted in the southern city of Deraa. The government's use of deadly force to crush the dissent soon triggered nationwide protests demanding the president's resignation.
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| Protests in the southern city of Deraa in March 2011 were suppressed by security forces
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As the unrest spread, the crackdown intensified. Opposition supporters
began to take up arms, first to defend themselves and later to expel
security forces from their local areas. Mr Assad vowed to crush
"foreign-backed terrorism" and restore state control.
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| The city of Homs, dubbed "the capital of the revolution" suffered widespread destruction
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The violence rapidly escalated and the country descended into civil war
as hundreds of rebel brigades were formed to battle government forces
for control of the country.
Why has the war lasted so long?
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| Government forces have lost control of large swathes of the country to various armed groups |
In essence, it has become more than just a battle between those for or against Mr Assad.
A key factor has been the intervention of regional and world powers, including Iran, Russia, Saudi Arabia and the United States. Their military, financial and political support for the government and opposition has contributed directly to the intensification and continuation of the fighting, and turned Syria into a proxy battleground.
External powers have also been accused of fostering sectarianism in what
was a broadly secular state, pitching the country's Sunni majority
against the president's Shia Alawite sect. Such divisions have
encouraged both sides to commit atrocities that have not only caused
loss of life but also torn apart communities, hardened positions and
dimmed hopes for a political settlement.
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| The northern Syrian city of Raqqa is the headquarters of the jihadist group Islamic State (IS)
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Jihadist groups have also seized on the divisions, and their rise has
added a further dimension to the war. Hayat Tahrir al-Sham, an alliance
formed by what was once the al-Qaeda-affiliated al-Nusra Front,
controls large parts of the north-western province of Idlib.
Meanwhile,
so-called Islamic State (IS), which controls large swathes of northern
and eastern Syria, is battling government forces, rebel brigades and
Kurdish militias, as well as facing air strikes by Russia and a US-led
multinational coalition.
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| Thousands of Iranian-backed Shia militiamen are supporting Syrian government forces
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Thousands of Shia militiamen from Iran, Lebanon, Iraq, Afghanistan and
Yemen say they are fighting alongside the Syrian army to protect holy
sites.
Why are so many outside powers involved?
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| Russia's air campaign aimed to "stabilise" the government of President Bashar al-Assad
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Russia, for whom President Assad's survival is critical to
maintaining its interests in Syria, launched an air campaign in
September 2015 with the aim of "stabilising" the government after a
series of defeats. Moscow stressed that it would target only
"terrorists", but activists said its strikes mainly hit Western-backed
rebel groups.
Six months later, having turned the tide of the war
in his ally's favour, President Vladimir Putin ordered the "main part"
of Russia's forces to withdraw, saying their mission had "on the whole"
been accomplished. However, intense Russian air and missile strikes went
on to play a major role in the government's siege of rebel-held eastern
Aleppo, which fell in December 2016.
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| Rebels have received only limited military assistance from Western powers
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Shia power Iran is believed to be spending billions of dollars a year
to bolster the Alawite-dominated government, providing military
advisers and subsidised weapons, as well as lines of credit and oil
transfers. It is also widely reported to have deployed hundreds of
combat troops in Syria.
Mr Assad is Iran's closest Arab ally and
Syria is the main transit point for Iranian weapons shipments to the
Lebanese Shia Islamist movement Hezbollah, which has sent thousands of
fighters to support government forces.
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| A US-led coalition has been conducting air strikes on Islamic State militants in Syria since 2014
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The US, which says President Assad is responsible for widespread
atrocities, has provided only limited military assistance to "moderate"
rebel groups, fearful that advanced weapons might end up in the hands of
jihadists. Since September 2014, the US has conducted air strikes on IS
in Syria, but says it has not intentionally attacked government forces.
Sunni-ruled
Saudi Arabia, which is seeking to counter the influence of its rival
Iran, has been a major provider of military and financial assistance to
the rebels, including those with Islamist ideologies.
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| Turkish troops are backing a Syrian rebel offensive to take control of a northern border area
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Turkey is another staunch supporter of the rebels. However, it has
sought to contain the Kurdish Popular Protection Units (YPG) militia
whose fighters are battling IS as part of the US-backed Syrian
Democratic Forces (SDF) alliance. Ankara accuses the YPG of being an
extension of the banned Turkish Kurdistan Workers' Party (PKK).
In
August 2016, Turkish troops backed a rebel offensive to drive IS
militants out of one of the last remaining stretches of the Syrian side
of the border not controlled by the Kurds. Since then, they have taken
control of some 2,000 sq km (772 sq miles) of territory, according to
the Turkish military, and forced the US to deploy troops to the
SDF-controlled town of Manbij to prevent clashes.
What impact has the war had?
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| There are no reliably accurate statistics on the number of people killed or wounded in the fighting
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The UN says at least 250,000 people have been killed in the past five
years. However, the organisation stopped updating its figures in August
2015. The Syrian Observatory for Human Rights, a UK-based monitoring
group, puts the death toll at more than 321,000, while a think-tank
estimated in February 2016 that the conflict had caused 470,000 deaths, either directly or indirectly.
Five million people - most of them women and children -
have fled Syria,
according to the UN. Neighbouring Lebanon, Jordan and Turkey have
struggled to cope with one of the largest refugee exoduses in recent
history.
About 10% of Syrian refugees have sought safety in Europe, sowing
political divisions as countries argue over sharing the burden. A
further 6.3 million people are
internally displaced inside Syria.
The UN
estimates
it will need $3.4bn (£2.7bn) to help the 13.5 million people who will
require some form of humanitarian assistance inside Syria in 2017.
Almost 85% of Syrians
live in poverty,
with more than two-thirds of the population in either extreme or abject
poverty. More than 12.8 million people in Syria require health
assistance and more than seven million are food insecure amid rising
prices and food shortages. Households spend up to a quarter of their
income just on water. Some 1.75 million children are out of school.
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| Almost half of Syria's pre-war population of 23 million has been displaced by the war
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The warring parties have compounded the problems by refusing
humanitarian agencies access to many of those in need. Some 4.9 million
people live in besieged or hard-to-reach areas.
What's being done to end the conflict?
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| Previous attempts by the UN to broker a political settlement have failed
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With neither side able to inflict a decisive defeat on the other, the
international community long ago concluded that only a political
solution could end the conflict. The UN Security Council has called for
the implementation of the
2012 Geneva Communique, which envisages a transitional governing body with full executive powers "formed on the basis of mutual consent".
Peace
talks in early 2014, known as Geneva II, broke down after only two
rounds, with the UN blaming the Syrian government's refusal to discuss
opposition demands.
A year later, the conflict with IS lent fresh
impetus to the search for a political solution in Syria. The US and
Russia persuaded representatives of the warring parties to attend
"proximity talks" in Geneva in January 2016 to discuss a Security
Council-endorsed road map for peace, including a ceasefire and a
transitional period ending with elections.
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| A local truce in the Homs suburb of al-Wair in December 2015 allowed rebels to be evacuated
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The first round broke down while still in the "preparatory" phase, as
government forces launched an offensive around Aleppo. The talks
resumed in March 2016, after the US and Russia brokered a nationwide
"cessation of hostilities" that excluded jihadist groups. But they
collapsed the following month.
Turkey and Russia brokered another
truce after the fall of Aleppo. In January 2017, they and Kazakhstan
hosted the first face-to-face meeting between rebel fighters and
government officials since the war began. That was followed by a fresh
round of UN-mediated talks in Geneva, which UN envoy Staffan de Mistura
said "achieved much more than many people had imagined we could have".
What is left of rebel territory?
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| Several opposition-held districts and suburbs of Damascus are under siege
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The fall of Aleppo means the government now controls Syria's four
biggest cities. But large parts of the country are still held by other
armed groups.
Rebel fighters and allied jihadists are estimated to control about 15% of Syrian territory,
according to the Syrian Observatory for Human Rights.
US officials
said
in early December 2016 that there were 50,000 or more "moderate"
rebels, concentrated in the north-western province of Idlib and the
western Aleppo countryside.
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| Al-Qaeda-linked jihadists are a key part of the rebel alliance controlling Idlib province
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Rebels also control smaller areas in the central province of Homs,
the southern provinces of Deraa and Quneitra, and the eastern Ghouta
agricultural belt outside Damascus.
Kurdish forces, who say they
support neither the government nor the opposition, meanwhile control
much of Syria's border with Turkey, as well as a large part of the
country's north-east.
And although they have suffered extensive
losses in the past two years, IS militants still hold large parts of
central and northern Syria, including the city of Raqqa.
