Who are the key players in Turkey's Syria offensive, and what's at stake?

Turkish forces began a military operation in northeast Syria on Wednesday, shortly after U.S. troops began vacating the region. The newest front in the Middle East could have ripple effects on everything from the strength of ISIS to the impeachment proceedings against U.S. President Donald Trump.

Who are the key players in the offensive and what's at stake? CBC News explains the offensive:

Why is Turkey attacking Syria?

Turkey isn't attacking Syria's central government, but instead wants to eliminate what it sees as a terrorist threat on its border: Kurdish fighters in Syria.

The Kurds are an ethnic minority spread across several countries in the region, and Turkey says the Kurdish militia in northeastern Syria, known as the People's Protection Units, or YPG, is allied with outlawed Kurdish rebels fighting inside Turkey.

Turkey also says it plans to create a "safe zone" to resettle millions of Syrian refugees currently living on Turkish soil who have fled during Syria's yearslong civil war. This would then serve as a buffer against the YPG.

Who are the Kurds?

The Kurdish ethnic minority, mainly Sunni Muslims, speaks a language related to Farsi and lives mostly in a mountainous region straddling the borders of Armenia, Iraq, Iran, Syria and Turkey. The latter four countries all have large Kurdish minorities seeking varying degrees of autonomy from central governments after decades of repression.

During the ongoing Syrian civil war, Syrian President Bashar al-Assad focused on crushing mainly Sunni Arab rebels, turning a blind eye as Kurdish fighters carved out self-rule across the north and east. Kurdish forces control about a quarter of the country's territory — the biggest chunk of Syria not in state hands — with its own forces and bureaucracy.

Syrian Kurdish leaders say they don't want to separate but want regional autonomy.

Why attack now?

Because Trump pulled his country's soldiers — just a few dozen of them — from the area.

Turkey's offensive — named Operation Peace Spring — came after Trump agreed to withdraw American troops, paving the way for an assault on Kurdish forces that have long been allied with the United States in the fight against Islamic State in Iraq and Syria (ISIS).

Trump's move isn't popular with either Republicans or Democrats, but the president has said "stupid endless wars, for us, are ending!"

Could this affect ISIS?

It could, according to experts. The U.S. had hoped to train the Syrian Democratic Forces (which is spearheaded by YPG) and other groups to create a stabilization force of 50,000 to 60,000 fighters to help prevent a resurgence of ISIS.

As of last month, the U.S. military estimated it was about halfway toward that goal.

One official told Reuters that the SDF was still guarding prisons holding some 11,000 captured Islamic State fighters, but noted that a small number of SDF forces had relocated ahead of the Turkish offensive.

How do those not directly involved feel about it?

Generally, not good.

First, Trump's decision to withdraw from Syria drew widespread condemnation internationally and across party lines within the U.S. because it is widely seen as abandonment of the Kurdish fighters who have been the U.S. Armed Forces' sole allies in Syria.

Turkey's quick attacks drew sharp criticism from many quarters, including Germany, the European Union and Canada.

"Canada firmly condemns Turkey's military incursion into Syria today," Foreign Affairs Minister Chrystia Freeland said on Twitter.

There has also been no public support from Turkey's Western allies for its plan to resettle two million Syrians in northeast Syria.

Iran and Russia are both key allies of the Assad government and have troops on the ground in Syria. While they may publicly oppose a Turkish incursion, they probably don't mind an operation that diminishes the Kurdish forces.

Beyond the loss of life, what are the risks?

Broadly, there are fears the incursion could inflame further conflicts in Syria and the region, potentially allowing for a revival of ISIS, as well as another surge of Syrian refugees.

Both could be a problem for countries that have already spent recent years dealing with large numbers of refugees, as well as the politically thorny question of what to do about ISIS members who are also Western citizens. 

For Turkey, there are further dangers, including alienating fellow NATO members or getting bogged down in a long conflict with the battle-hardened Kurdish fighters.

And for Trump, there is the challenge of angering Republicans at a time when he needs their support due to the ongoing impeachment inquiry.