ROOTS OF THE SYRIA CRISIS, AND HOW U.S. GOT INVOLVED

How it began, why it got complicated and what may come next.

The Syrian war has been a slowly unfolding catastrophe, one that has embroiled nearly the whole world. Here’s a look at how it started, why it became so complicated and what might happen next.

How did the war in Syria start?

It’s hard to remember now, but the unrest in Syria began on a hopeful note.

In March 2011, peaceful protests broke out around the country as part of the Arab Spring uprisings. Organizers called on Syrian President Bashar Assad to make democratic reforms, but his government responded with violence.

In response, some of the protesters teamed up with military defectors to form the Free Syrian Army, a rebel group that wanted to overthrow the government. By 2012, this armed struggle had devolved into a full-blown civil war.

So how did this go from a civil war to an international crisis?

For one, Syria is critical to Iran’s regional power plays. Iran needs Syria to move its weapons and proxy militias to other allies. So when Assad seemed threatened, Iranian leaders sent Hezbollah, its Shiite allies in Lebanon, to aid the Syrian government.

At the same time, Iran’s Sunni rivals in the region — Qatar, Saudi Arabia and Turkey

among them — began sending arms and money to anti-Assad rebels, including extremist militias.

Russia, meanwhile, remained steadfast in its long-standing support for Assad’s government. According to one scholar, Russia helped build the modern Syrian military, and Assad is one of Russian President Vladimir Putin’s strongest allies in the Middle East. Russia has often blocked meaningful international action on Syria by vetoing proposals at the U.N. Security Council, and Moscow changed the course of the war in Assad’s favor with a military intervention in 2015.

What has life been like for Syrians?

In short: a nightmare. Since the start of the war, more than 465,000 Syrians have been killed, 1 million more have been injured and 12 million — more than half the country’s population — have been forced to flee their homes. More than 5.5 million have moved abroad and registered as refugees.

Why is the United States involved?

The United States has been reluctant to become too entangled in Syria, but it has acted for two main reasons.

First, the Islamic State began developing a foothold in the country in 2013.

The next year, the United States formed an international coalition to launch airstrikes against the group. It eventually sent ground troops into the fight, and about 2,000 U.S. forces are now deployed there.

The United States also has acted to punish the Assad government for using chemical weapons such as sarin and chlorine gas. In 2012, President Barack Obama called the use of chemical weapons a “red line” that would prompt military intervention. But when a sarin gas attack in the Damascus suburbs of Eastern Ghouta killed about 1,400 people a year later, according to the U.S. government’s assessment,

Obama backed away from a strike.

Instead, the U.N. Security Council ordered Assad to destroy his chemical-weapons stockpile and sign the Chemical Weapons Convention, which prohibits countries from producing, stockpiling or using chemical weapons.

But there have been several reports of chemical-weapons attacks since then. One particularly bad strike took place on April 4, 2017. Nearly 100 people were killed in the northern town of Khan Sheikhoun in an apparent sarin attack. It garnered worldwide headlines and the attention of President Donald Trump,

who expressed horror at the images of “innocent children, innocent babies” poisoned by a nerve agent.

Just a few days after that attack, Trump authorized a cruise-missile strike on a Syrian air base. It was the first direct U.S. strike on the Syrian regime in the entire war.

But that apparently hasn’t stopped Assad from using chemical weapons. So what’s next?

Just a couple of days ago, the Assad government was once again accused of using chemical weapons on civilians in Eastern Ghouta, a rebel-controlled area outside of Damascus. Forty people died. On Twitter, Trump threatened a military response, but it’s not clear when that would happen or what it would look like. On Thursday morning, he tweeted that he “never said when an attack on Syria would take place. Could be very soon or not so soon at all!”

It’s unclear what will come next.

ANAS ALKHARBOUTLI / DPA Syrians are evacuated in March from Zamlka in Eastern Ghouta province, once Syria’s main rebel bastion, but anti-regime fighters put down arms after a deal assured them and their families’ safe passage to northern Syria.

HUSSEIN MALLA / AP U.S. forces appear at a newly installed position April 4 near the front line between U.S.-backed Syrian Manbij Military Council and Turkishbacked fighters in Manbij, north Syria.