Syria has been engulfed in a devastating civil war since 2011 after Syrian President Bashar Assad lost control over large parts of the country to multiple revolutionary groups. The conflict has since drawn in foreign powers and brought misery and death to Syrians.

Syria's army, officially known as the Syrian Arab Army (SAA), is loyal to Syrian President Bashar al-Assad and is fighting to restore the president's rule over the entire country. The SAA has been fighting alongside a number of pro-Assad militias such as the National Defense Force and has cooperated with military advisors from Russia and Iran, which back Assad.

Turkey, which is also part of the US-led coalition against IS, has actively supported rebels opposed to Assad. It has a tense relationship with its American allies over US cooperation with Kurdish fighters, who Ankara says are linked to the Kurdistan Workers' Party (PKK) fighting in Turkey. Turkey has launched multiple military offensives targeting Kurdish militias.

The Kremlin has proven to be a powerful friend to Assad. Russian air power and ground troops officially joined the fight in September 2015 after years of supplying the Syrian army. Moscow has come under fire from the international community for the high number of civilian casualties during its airstrikes. However, Russia's intervention turned the tide in war in favor of Assad.

A US-led coalition of more than 50 countries, including Germany, began targeting IS and other terrorist targets with airstrikes in late 2014. The anti-IS coalition has dealt major setbacks to the militant group. The US has more than a thousand special forces in the country backing the Syrian Democratic Forces.

The Free Syrian Army grew out of protests against the Assad regime that eventually turned violent. Along with other non-jihadist rebel groups, it seeks the ouster of President Assad and democratic elections. After suffering a number of defeats, many of its members defected to hardline militant groups. It garnered some support from the US and Turkey, but its strength has been greatly diminished.

Fighting between Syrian Kurds and Islamists has become its own conflict. The US-led coalition against the "Islamic State" has backed the Syrian Democratic Forces, an alliance of Kurdish and Arab militias. The Kurdish YPG militia is the main component of the SDF. The Kurds have had a tacit understanding with Assad.

"Islamic State" (IS) took advantage of regional chaos to capture vast swathes of territory in Iraq and Syria in 2014. Seeking to establish its own "caliphate," IS has become infamous for its fundamentalist brand of Islam and its mass atrocities. IS is on the brink of defeat after the US and Russia led separate military campaigns against the militant group.

IS is not the only terrorist group that has ravaged Syria. A number of jihadist militant groups are fighting in the conflict, warring against various rebel factions and the Assad regime. One of the main jihadist factions is Hay'at Tahrir al-Sham, which controls most of Idlib province and has ties with al-Qaeda.

Iran has supported Syria, its only Arab ally, for decades. Eager to maintain its ally, Tehran has provided Damascus with strategic assistance, military training and ground troops when the conflict emerged in 2011. The Iran-backed Lebanese Shiite militant group Hezbollah also supports the Assad regime, fighting alongside Iranian forces and paramilitary groups in the country.

In 2011, as regimes crumble across the region, tens of thousands of Syrians take to the streets to protest against corruption, high unemployment and soaring food prices. The Syrian government responds with live ammunition, claiming some 400 lives by May.

At the urging of Western countries, the UN Security Council condemns the violent crackdown. The EU and US implement an arms embargo, visa bans and asset freezes in the months that follow. With the backing of the Arab League, calls eventually grow for the Syrian president's departure. But not all UN members agree with this demand.

Bashar al-Assad - who has been in power since the death of his father in 2000 - sees his reputation wane with the continuing unrest. He refuses to end decades-long emergency rule, which allows for surveillance and interrogation. Russia backs its ally, supplying weapons and vetoing UN resolutions on Syria multiple times.

By the end of the year, human rights groups and the UN have evidence of human rights abuses. Civilians and military deserters are slowly beginning to organize themselves to fight back against government forces, which have been targeting dissidents. More than 5,000 have died so far in the fighting. It will take another six months before the UN acknowledges that a war is taking place on Syrian soil.

In September 2012, Iran confirms that it has fighters on the ground in Syria - a fact long denied by Damascus. The presence of allied troops underscores the hesitance of the US and other Western powers to intervene in the conflict. The US, stung by failed interventions in Afghanistan and Iraq, sees dialogue as the only reasonable solution.

As the death toll nears 100,000, the number of refugees in neighboring countries - such as Turkey and Jordan - hits one million. That number will double by September 2013. The West and the Arab League have seen all attempts at a transitional government fail in the two years of war, watching as fighting spills over into Turkey and Lebanon. They fear Assad will stay in power by any means possible.

Assad has long claimed he's combatting terrorists. But it's not until the second year of war that the fragmented Free Syrian Army is definitely known to include radical extremists. The group Al-Nusra Front pledges allegiance to al Qaeda, further splintering the opposition.

In June 2013, the White House says it has evidence that Assad has been using sarin nerve gas on civilians - a report later backed by the UN. The discovery pushes US President Barack Obama and other Western leaders toward considering the use of military force. However, Russia's proposal to remove the chemical weapons ultimately wins out.

Reports of a new jihadist group calling itself the Islamic State of Iraq and the Levant (ISIL) emerge in the final weeks of 2013. Taking land in northern Syria and Iraq, the group sparks infighting among the opposition, with some 500 dead by early 2014. The unexpected emergence of IS ultimately draws the US, France, Saudi Arabia and other nations into the war.

The "Islamic State" (IS) — also known as ISIL, ISIS and Daesh — is an al-Qaida splinter group with a militant Sunni Islamist ideology. It emerged in the aftermath of the US-led invasion of Iraq in 2003 and is led by Abu Bakr al-Baghdadi. Their goal is to create a worldwide "caliphate." It gained worldwide notoriety in 2014 after a blitzkrieg military campaign that resulted in the capture of Mosul.

IS is believed to be operational in more than a dozen countries across the world. It controls territories in Iraq and Syria. However, the group has lost much of the territory it controlled in Iraq and Syria at the height of its expansion in 2014.

The US leads an international coalition of more than 50 countries, including several Arab nations. Russia, Iran and its Lebanese Shiite ally Hezbollah, which all support the Syrian government, also fight IS. Regional forces such as the Kurdish peshmerga (above) and US-backed Syrian Kurdish fighters, fight IS on the ground. The Iraqi army and militia have pushed IS from large parts of the country.

One of IS' main sources of income has been oil and gas. At one point, it controlled an estimated one-third of Syria's oil production. However, US-led airstrikes deliberately targeted oil resources and the Syrian government as well as US-backed Syrian Kurdish fighters have retaken most oil wells. Other means of income include taxes, ransom, selling looted antiquities and extortion.

IS has claimed responsibility for numerous terrorist attacks across the globe. The militant group has targeted capitals across the EU, including Berlin, Brussels and Paris. IS leaders have encouraged so-called "lone wolf" attacks, whereby individuals who support IS carry out terrorist acts without the direct involvement of the group.

The group uses various tactics to expand its power. IS fighters have looted and destroyed historical artifacts in Syria and Iraq in an attempt at "cultural cleansing." The group has also enslaved thousands of women from religious minority groups, including Yazidis. IS also uses a sophisticated social network to distribute propaganda and recruit sympathizers.

IS has further exacerbated the ongoing Syrian conflict. Millions of Syrians and Iraqis have fled their homes, many traveling to Europe in pursuit of refuge. Although it has lost all of its strongholds, the militant group has left extraordinary destruction in its wake. Areas affected by the militant group's rule will likely take years to rebuild.

May 16, 2017: Trump welcomes Erdogan to Washington, saying both presidents have a "great relationship" and would make it "even better." Erdogan congratulates Trump on his "legendary" 2016 election win but complains bitterly about US arming of the Kurdish YPG militia, claiming that its inclusion in the US-led campaign against IS in in war-torn Syria provides a cover for Kurdish separatism.

May 17: As Erdogan ends his visit, Voice of America video footage emerges showing his guards assaulting Kurdish protesters outside the Turkish ambassador's residence in Washington. A month later, US authorities issue arrest warrants for 12 members of Erdogan's security detail, who had long returned to Turkey. US Secretary of State Rex Tillerson says the assaults breached "legitimate" free speech.

July 15, 2017: Turkey marks the first anniversary of the failed coup attempt. In a post-coup bid crackdown 50,000 people were arrested, accused of links to the US-based cleric Fethullah Gulen, an Erdogan ally-turned-rival. Tens of thousands more face job suspensions. The refusal of the US to extradite Gulen has been a major sore spot in relations.

August 23: US Defense Secretary James Mattis visits Ankara as the Pentagon stresses US commitment to bilateral relations and "honest dialogue." Mattis had just visited Iraq to assess the anti-IS campaign. Erdogan tells Turkish media that Turkey will thwart any attempt by the Kurdish People's Protection Units (YPG) to establish a "terror corridor" in northern Syria through to the Mediterranean.

October 5: Turkish authorities arrest Metin Topuz, a Turkish national employed at the US consulate in Istanbul. He is formally charged with espionage and collaboration in the 2016 coup attempt. The US embassy in Ankara subsequently says it is "deeply disturbed" by the arrest. It's reportedly the second since March, when a Turkish US consulate employee was arrested in Adana.

October 8-9: The United States suspends its issuance of non-immigrant visa applications to Turkish nationals, saying it has to "reassess" Turkish readiness to respect security at US diplomatic missions. Turkey suspends its visa services for US nationals and summons another staffer at the US consulate in Istanbul.

November 6: The US Embassy in Ankara announces that it is reinstating its visa program for Turkish tourists on a "limited" basis after receiving assurances from the government that no employees will be detained "for carrying out official duties." Shortly thereafter, Turkey confirms that it is also resuming visa services for US citizens one day before Prime Minister Yildirim visits Washington.

December through August, 2018: In December, Turkey announced it would buy the Russian S-400 missile system, which is incompatable with NATO systems. The US Congress has included a provision in a defense bill that would cut Turkey out of the F-35 fighter jet program if it moves forward with the S-400 deal.

August 1, 2018: The US sanctions Turkey's interior and justice ministers over the continued detention of pastor Andrew Brunson. Brunson had been moved from prison to house arrest in late July, but that fell short of US demands for his immediate release and end to terror and espionage charges. Brunson was arrested almost two years ago.