(Photo: Remy de la Mauviniere/AP)

President Bashar al-Assad

Assad's father, who came from a poor Alawite family, seized power in a 1970 coup. Hafez al-Assad ruled Syria with a firm hand and was accused of numerous human rights abuses over the years.

Bashar Assad presented himself as a reformer when he succeeded his father in 2000. But critics have called any changes largely superficial, and Assad's crackdown on protests in March 2011 sparked the current civil war.

Support for Bashar Assad has held firm among the Alawite minority, who make up about 12 per cent of the country's population. Much of the Christian minority have also backed Assad in the past, preferring his secular rule to an Islamist alternative.

(Photo: Christian Hartmann/Reutervs)

Syrian opposition

After days of intense talks in Qatar, and under mounting international pressure, Syria's scattered anti-government groups struck a deal to form a unified opposition in November 2012.

The Syrian National Coalition for Opposition and Revolutionary Forces was designed to bring together members of various religious sects opposed to Assad.

The U.S. and dozens of other countries have officially recognized the coalition as the sole representative of the Syrian people. (Canada has not yet followed suit.)

Veteran dissident Ahmad Jarba, pictured, became the group's new president in July 2013. A member of a prominent eastern Syrian tribe, Jarba also is reported to have close ties to Saudi Arabia.

(Photo: Burhan Ozbilici/AP)

Free Syrian Army

As anti-regime demonstrations heated up in summer 2011, members of Assad's army began to defect to the protesters' side. These officers and soldiers eventually formed the nucleus of the Free Syrian Army, the main armed group opposed to Assad.

Thousands of further defections and volunteer signups propelled the FSA's growth over the next year. But it faces a challenge as Assad's army is attempting to stem the tide and prevent others from leaving.

Many Western nations cannot shake their concerns that by supplying weapons to the FSA, they could aggravate the war and munitions could fall into the wrong hands — namely religious extremists.

(An al-Nusra flag. Manu Brabo/AP)

Jihadist groups

Al-Qaeda-linked groups have claimed responsibility for suicide bombings on Syrian government targets during the civil war.

In December 2012, the U.S. declared the jihadist Jabhat al-Nusra to be a terrorist group in an effort to blunt the influence of extremists in the Syrian opposition.

Al-Nusra's leader formally declared his loyalty to al-Qaeda in spring 2013. But it has resisted a merger with another al-Qaeda group, the Islamic State of Iraq and Syria (ISIS), which has expanded its operations into Syria. (Al-Qaeda cut ties with ISIS in February 2014.)

These groups have fought each other, as well as the Free Syrian Army — signs of deepening cracks in the opposition movement.

(Members of Hezbollah shout slogans. Hussein Malla/AP)

Hezbollah

The leader of Lebanon's Hezbollah has vowed that his Shiite militant group will not stand idly by while its chief ally in Damascus is under attack.

Sheikh Hassan Nasrallah said Hezbollah members are fighting in Syria against Islamic extremists who pose a danger to Lebanon, and pledged that his group will not allow Syrian militants to control areas that border Lebanon.

Syria, along with Iran, has been the main backer of Hezbollah and much of the group's arsenal consisting tens of thousands of rockets is believed to have come through or from Syria.

(Photo: Erik Hillbom/Scanpix Sweden/AP)

UN weapons inspectors

UN Secretary General Ban Ki-moon authorized a fact-finding tour to investigate allegations of chemical weapons use in Syria. After four months of behind-the-scenes talks, the Assad regime approved the terms for the mission in July 2013.

Syrian activists and opposition leaders say chemical weapons were used in an Aug. 21 attack that killed hundreds in the eastern Damascus suburbs. Assad has been quoted as saying the claims are "nonsense."

In their initial findings, presented on Sept. 16, the inspectors said that chemical weapons had been used on a "large scale" but the report did not say who launched the attack.

The team, led by Swedish professor Ake Sellstrom (pictured) said in a December 2013 report that chemical weapons were likely used in four other locations.

U.N. Secretary-General Ban Ki-moon, left, speaks at OPCW offices in The Hague in April 2013. (Jan-Joseph Stok/AP)

Organization for the Prohibition of Chemical Weapons

The organization (OPCW) is responsible for implementing the Chemical Weapons Convention, which came into force in 1997. The international agreement bans the production, storage and/or use of chemical weapons and their precursors.

Syria signed on to the convention as part of a September 2013 Russia-U.S. deal to avoid military punishment for alleged chemical weapons use.

The Assad regime submitted its chemical weapons inventory to the OPCW, as demanded, on Sept. 20. Destruction of the stockpile is ongoing. All chemical weapons and related components must be removed from Syria by mid-2014.

OPCW was awarded the 2013 Nobel Peace Prize on Oct. 11.

(Photo: Carolyn Kaster/AP)

U.S.

In August 2012, President Barack Obama said the U.S. would reconsider its opposition to military involvement in the Syrian civil war if Assad's regime deployed or used chemical or biological weapons. He called such action a "red line" for the United States.

In June 2013, U.S. officials said that line had been crossed. They reported that Syria has used sarin gas on multiple occasions, killing up to 150 people.

Shortly after, Obama authorized sending weapons to the Syrian rebels for the first time.

A purported chemical attack in August 2013 pushed the U.S. even closer to action.

Obama labelled the alleged attack an "assault on human dignity" and called for direct military action in Syria. However, he agreed to pursue a diplomatic solution backed by Russia before launching any strikes.

Russia

Russia is one of Syria's most important international allies. Syria has been among Russia's top customers for international arms exports, with contracts in the billions, according to reports. The trade, while legal, raised concerns over whether Russia was arming Assad's regime with weapons to use against the rebels.

An official said in July 2012, however, that Russia would not deliver weapons to Syria while the situation remains unresolved. And by December, as Assad's grip weakened, Moscow sought to distance itself from the regime.

In June 2013, President Vladimir Putin told Obama that Russian and U.S. positions on Syria do not "coincide". But the two leaders said during that month's G8 summit that they shared an interest in stopping the violence.

Russia firmly opposed the American plan for military action after the August 2013 chemical weapons accusations. It backed a diplomatic solution that saw the Assad regime turn over its chemical arsenal.

U.K.

British politicians voted against a military response in Syria on Aug. 29, 2013. Prime Minister David Cameron, pictured, lost the vote with 285 against the idea compared to 272 in favour.

Cameron said he "strongly" believes in the need for a tough response to alleged chemical weapons use, but also believes in respecting the will of the House of Commons.

The U.K. vote was not binding, but in practice the rejection of military strikes effectively tied Cameron's hands.

In the days leading up to the vote, the U.K. had seemed a likely participant, along with the U.S. and several other allies, in a possible military strike against the Assad regime.

(Photo: Jeff Christensen/Reuters)

UN Security Council

The five permanent members of the United Nations body remain split on how to confront the Assad regime. Russia and China have repeatedly blocked efforts by Western countries such as the U.S. to condemn Syria or impose sanctions for government attacks on civilians.

The council did unanimously approve a statement condemning Syria's October 2012 shelling of a Turkish town "in the strongest terms."

Before a diplomatic solution emerged, it was also deadlocked on how to respond to August 2013 accusations of chemical weapons use by Assad's regime.

Egypt

Mohammed Morsi, then Egypt's Islamist president, announced on June 15, 2013, that he was cutting off diplomatic relations with Syria and closing Damascus' embassy in Cairo. The decisions were made amid growing calls from hard-line Sunni clerics in Egypt and elsewhere to launch a "holy war" against Syria's embattled regime.

Morsi also called on Lebanon's Hezbollah to leave Syria.

But weeks later, Morsi was ousted as president, leaving Egypt in the hands of an interim government. And that government has signalled a change in direction.

Egypt's foreign minister told reporters in July that "there are no intentions for jihad in Syria," while still supporting a change of regime in the country.

The country refused to back a military strike on Syria and has urged the warring parties to launch peace talks.

Turkey

Relations with Syria had been strained for decades, but the chilliness thawed somewhat throughout the 2000s. The uprising and civil war have changed all that.

Syrian forces have shot down a Turkish military jet near the countries' shared border; the Syrian government maintains the flight had violated its airspace.

The latest blow to relations came in May 2013: Turkey accused a group with links to the Syrian intelligence service of setting off car bombs that killed 46 people in a Turkish border town. Syria has rejected allegations it was behind the attacks.

Turkey has said it will defend its interests by force if necessary, and has received the backing of its NATO allies.

Israel

A top Israeli military intelligence official said in April 2013 that the Assad regime used chemical weapons the previous month in its battle against insurgent groups.

The claim was based on visual evidence of alleged attacks. It was the first time that a senior Israeli official had levelled such an accusation against the Syrian regime.

Israel launched an airstrike against a suspected Syrian weapons site in May 2013.

(Photo: David Karp/AP)

Lakhdar Brahimi

Brahimi, a former Algerian foreign minister and longtime UN diplomat known as a strong-willed broker, became the UN-Arab League special envoy for Syria in August 2012.

He replaced Kofi Annan, the UN's former secretary general.

Annan said most of the blame for the stalemate falls on the Syrian government for its continued refusal to implement his peace plan. But he also chastised the UN Security Council for continuing to feud while the bloodshed continues in the battle-scarred country.

(Iraqi PM Nouri al-Maliki. Khalid Mohammed/AP)

Iraq

Dozens of Syrian regime soldiers were killed in an ambush inside Iraqi territory in March 2013, amid heightened concerns that Iraq could be drawn into Syria's civil war.

The fact that the soldiers were on Iraqi soil in the first place raises questions about Baghdad's apparent willingness to quietly aid the Assad's embattled regime.

Iraqi Prime Minister Nouri al-Maliki, pictured, has told The Associated Press that he feared a victory for the anti-Assad side would create a new extremist haven and destabilize the wider Middle East.

His comments reflect fears by many Shiite Muslims that Sunnis would come to dominate Syria should Assad be toppled. Assad's regime is backed by Shiite powerhouse Iran, which has been building ties with the Shiite-led government in Baghdad in recent years.

(Photo: Reuters)

Friends of Syria

The group of more than 100 countries came together in February 2012 at the initiative of former French president Nicolas Sarkozy. Canada has been among the participants.

The Friends of Syria has called for tougher international sanctions against the Assad regime.

At the group's fourth meeting, in Morocco in December (pictured), many countries officially recognized Syria's new opposition group as the sole representative of the Syrian people.

(Photo: Majed Jaber/Reuters)

Riad Hijab

Hijab, Assad's prime minister, has been the most prominent political member of the regime to defect.

"The regime is on the verge of collapse morally and economically," Hijab told a news conference after fleeing to Jordan with his family in August 2012.

Other notable defectors include a commander with the elite Republican Guard and the country's ambassador to Iraq.

Other key Assad allies have been killed, including the president's brother-in-law and national security chief.

Saudi Arabia

Sunni-dominated Saudi Arabia has backed the opposition groups that are trying to topple Assad's Shiite regime.

It's suspected that the Saudis have even provided the opposition with arms, as have its allies in Qatar and Turkey.

The Saudis are also believed to have strong ties with opposition leader Ahmad Jarba.