Ignoring advice from his generals and advisers, Trump said that the U.S. would leave Syria.

Defense Department officials said that they were ordered to do it within 30 days.

[explosion]

Then came a flurry of criticism, even from inside his own party.

"I believe it is a catastrophic mistake."

"This is very disappointing."

"It needs to be reconsidered."

Then, the resignations.

First, Defense Secretary Jim Mattis quit.

And America's chief diplomat in the fight against ISIS, Brett McGurk, soon followed.

But now, the timeline is unclear.

"I never said we're doing it that quickly."

He went on to say that the U.S. will leave at a proper pace while continuing to fight ISIS, a shift from — “They're all coming back, and they're coming back now.”

The nearly eight-year-long war in Syria has left hundreds of thousands of people dead.

[explosion]

So, how did we get here and what are U.S. forces doing in Syria?

In 2011, uprisings rippled through the Middle East.

Leaders fell in Tunisia, Libya and Egypt.

And after months of anti-government protests in Syria, the U.S. had a message for President Bashar al-Assad: "This morning, President Obama called on Assad to step aside."

He didn't and the conflict escalated.

In 2012, Obama warned Assad against using Syria's stockpile of chemical weapons against his own people.

"That's a red line for us, and that there would be enormous consequences if we start seeing the use of chemical weapons."

A year later, Assad's army launched a chemical attack on a Damascus suburb, killing 1,400 people.

[screaming]

In response, the U.S. debated airstrikes, but they were avoided when Syria agreed to give up its chemical weapons.

But a new threat was also emerging — ISIS.

In 2014, the U.S. began supporting rebel groups to fight extremists, while also conducting airstrikes as part of an international coalition.

These efforts expanded and the U.S. troop numbers grew from hundreds to the low thousands.

In 2016, U.S.-supported fighters took control of the ISIS stronghold of Manbij — and in 2017 their de facto capital, Raqqa.

There are now around 2,000 American forces in Syria who are largely fighting alongside the Kurdish groups.

This has been a problem for America's ally Turkey, which has a long-standing conflict with the Kurds.

U.S. troops have had run-ins with Assad's forces as well as groups backed by Russia and Iran.

Since taking office, Trump has ordered two strikes on areas controlled by Assad in response to chemical weapons attacks.

"We are prepared to sustain this response, until the Syrian regime stops its use of prohibited chemical agents."

U.S. officials and allies dispute the claim that ISIS has been defeated.

They warn that an American departure will weaken U.S. influence in the region and may embolden Russia, Iran and Turkey, who are also on the ground.

The other worry? The move may inspire some ISIS fighters to return to Syria.