February 1, 1979: Ayatollah Ruhollah Khomeini returned to Tehran from exile in Paris. Euphoric Iranians greeted him at the airport as he touched down. For years, he had criticized the shah and the political elite in Iran for suppressing dissidents, for westernizing the country and for their extravagant lifestyles.

Around four million Iranians took to the streets to catch a glimpse of Khomeini’s motorcade as it headed to the central cemetery where he held his arrival speech. For around a year mass demonstrations against the Shah had been taking place. Since August 1978, widespread work stoppages by the opposition had crippled the country’s economy.

On January 16, 1979, Shah Reza Pahlavi left the country. At the Guadeloupe conference, attended by the leaders of four Western powers - the US, UK, France and West Germany - the shah lost support. Instead, the West talked of seeking dialogue with Khomeini. US President Jimmy Carter offered the shah asylum in the US - an offer he accepted.

The shah had previously appointed Shapour Bakhtiar, a leading member of the opposition National Front, to the position of interim prime minister to appease his opponents, but without success. Bakhtiar was expelled from the party for being appointed by the shah. Other party members had agreed to work only with Khomeini.

Khomeini declared on his arrival in Tehran that he did not recognize Bakhtiar’s government. From the airport he drove straight to Tehran’s central cemetery where he gave a gutsy speech before thousands of enthusiastic on-lookers. He disputed the monarchy and the parliament, saying it weakened legitimacy. Khomeini said that he alone would select Iran’s new government.

In Tehran and in other cities across the country violent clashes between revolutionaries and the shah’s supporters broke out. The street fighting went on for days and it was unclear which side had the upper hand. The military imposed a curfew, but most Iranian’s ignored it.

On February 5, 1979, Khomeini named Mehdi Bazargan from the National Front as the country’s transitional prime minister. At first it looked like the clergy would cooperate with the liberal opposition. However, disagreements between the two quickly escalated. Bazargan resigned on November 5, 1979, in response to the US embassy hostage situation in Tehran.

After Bazargan’s re-appointment, large numbers of Iranians took to the streets in support of the transitional government. The military declared it would not interfere with the power struggle. Shapour Bakhtiar had lost all support. He had to flee his home when armed Khomeini supporters intruded. In April, 1979, he went into exile in France.

Standing at attention for religious leaders: An elite unit of the Iranian Air Force greeted Ayatollah Ruhollah Khomeini. The Homafar unit played a major role in the revolution victory because they had allowed the public access to their arsenal during the civil unrest. On February 9, the Imperial Guard made a last ditch effort to attack the Homafar base.

Fighting between the Imperial Guard and the people intensified. On February 11, 1979, the regime collapsed: Revolutionaries occupied parliament, the Senate, the television broadcaster and other state-run institutions. Shortly thereafter, the fall of the monarchy was announced. To this day, Iranians celebrate February 11 as the anniversary of the 'Islamic revolution.’

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.