When Samer, a university student in Damascus, joined in the largest anti-government demonstrations so far in the capital Friday, he felt something he had never felt before. It was not fear, though he was afraid in the first few seconds.

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“After the first yelling, the first shout, you feel dignity,” said Samer, 24, who like many protesters did not want his surname used for fear of reprisals. “You feel that you are a real citizen, a real Syrian citizen.”

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Inspired by neighbors and technology, Syrians join in revolution, by Tara Bahrampour

2. THE REBELS

In July 2012, rebel forces penetrated Aleppo, Syria’s largest city and an Assad stronghold. The advance into the city symbolized the rising strength of the rebels and caused major alarm for the government. Hundreds of people were killed in clashes between the rebels and government-backed forces in the following months.

Like Damascus, the country's capital, Aleppo had long been seen as a bastion of government support. That the revolt is now spreading there represents another blow to the regime in a week that has seen its veneer of control in the country's two biggest cities shattered by the assassinations of four of its top security officials in a bombing.

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Syria’s two largest cities rocked by clashes, by Babak Dehghanpisheh and Liz Sly

3. THE CHEMICAL WEAPONS

Nearly 1,500 people, including more than 400 children, were killed when an area outside Damascus was hit with chemical weapons in August 2013. Images of the dead children, their bodies arranged in rows, became a major turning point in the conflict.

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Unknown to Syrian officials, U.S. spy agencies recorded each step in the alleged chemical attack, from the extensive preparations to the launching of rockets to the after-action assessments by Syrian officials.

4. THE ISLAMIC STATE

While the Syrian military was focused on quelling the insurgency, Islamic State fighters organized a Syria branch and began to claim territory in the region. In 2014, the Islamic State took full control of the city of Raqqa and declared it the capital of its self-proclaimed caliphate.

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At a time when the Islamic State is undergoing a revival in Iraq, killing more people there than at any time since 2008 and staging a spectacular jailbreak last month that freed hundreds of militants, the push into Syria signifies the transformation of the group into a regional entity.

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Al-Qaeda expands in Syria via Islamic State, by Liz Sly

5. THE REFUGEES

An estimated 11 million Syrians, half the prewar population, have been forced to leave their homes. Most have fled to countries in the region — Lebanon, Jordan, Turkey and Iraq — while more than 1 million have reached Europe.

Syrians are piled up on the streets of the Turkish port city of Izmir waiting for a place on one of the flimsy boats that will ferry them across the sea to Greece, and they say they have friends and family following behind.

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“Everyone I know is leaving,” said Mohammed, 30, who climbed three mountains to make his way across the Turkish border from the city of Aleppo with his pregnant wife, under fire from Turkish border guards. “It is as though all of Syria is emptying.”

'Syria is emptying,' by Liz Sly

6. THE RUSSIAN TROOPS

Russia's military launched airstrikes in Syria in September, significantly shifting the conflict in a way that some say favors the Assad regime. The strikes have complicated U.S. policy. President Vladimir Putin made a surprise announcement on Monday that he will pull out the “main part” of Russia's military from Syria.

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The strikes sharply increase tensions with Russia as U.S. officials dispute Moscow’s claim that its aircraft targeted the Islamic State. … Instead, U.S. officials said the strikes appeared to target opponents of Syria’s embattled President Bashar al-Assad, a key Russian ally.

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Russia begins airstrikes in Syria; U.S. warns of new concerns in conflict, by Andrew Roth, Brian Murphy and Missy Ryan

7. THE PARTIAL CEASE-FIRE

The list of warring factions in Syria is long. In addition to Russia's involvement, U.S.-backed rebels are fighting Iraqi and Lebanese militias, Kurdish forces are extending their reach, and the Islamic State continues to plague the region. A cease-fire sponsored by world powers went into effect, halting some of the fighting.

The unthinkable happened in Syria on Saturday as an internationally mandated truce unexpectedly took hold across much of the country, raising hopes that the beginning of an end to the five-year-old crisis may be in sight. ... For the first time in as long as anyone can remember, the guns were almost completely silent, offering Syrians a welcome respite from the relentless bloodshed that has killed in excess of a quarter of a million people.

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8. 'IT IS A MIRACLE THERE ARE ANY MODERATES LEFT AT ALL.'

Moderates who began the fight against the Assad regime are no longer the dominant fighting force. Instead, the Islamic State controls a large swath of territory and Assad remains in power.

In other countries, such as Egypt, autocratic regimes have reasserted their control with a vengeance, clamping down on liberties even more fiercely than had been the case before the demonstrations were held.

In all of them, except Tunisia, the moderates who dominated the early days of the revolts have been silenced, imprisoned, hunted down or driven into exile, either by the governments that sought to repress them or the extremists who moved into the vacuum created when state authority collapsed.