Here’s a look at what led up to the launch of the offensive by Turkey.
Why is Turkey fighting in Syria?
Erdogan has long wanted to launch a military operation into northeast Syria to create what he calls a “safe zone” on the Syrian side of the border with Turkey.
Erdogan’s goal is to force members of a Kurdish group called the YPG back away at least 20 miles from the border between Turkey and Syria.
The YPG, an acronym for the People's Protection Units, is a defense force made up of people from the Kurdish area of Syria. The YPG was formed after civil war broke out in Syria in 2011.
Erdogan said Wednesday that Turkey's aim was "to prevent the creation of a terror corridor across our southern border, and to bring peace to the area."
Why does Turkey want to push the YPG back and create a safe zone?
Turkish officials believe the YPG is an extension of a Kurdish rebel group called the Kurdistan Workers' Party (known as the PKK) that has for decades fought to disrupt the Turkish government. Erdogan’s government has labeled the YPG as a terrorist organization.
What do they want to do with the “safe zone?”
In addition to pushing back forces it sees as a terrorist threat, Turkey hopes to resettle at least 1 million of the 3.6 million Syrian refugees who fled the civil war in Syria and are living within Turkey’s borders.
Did they just decide to launch the offensive in the past weeks?
No, the United States has been working with Turkey and the YPG to allow for a "security mechanism" within the border area that would satisfy Turkey’s security concerns. The YPG was willing to cooperate by removing fortifications and weapons systems.
However, on Sunday, according to media reports, Erdogan told U.S. President Donald Trump that his country intended to move ahead with the offensive to push the Kurds back and resettle the Syrian refugees.
Who are the Kurds?
The Kurds are an ethnic minority group in the Middle East. They live in an area along the borders of Armenia, Iran, Iraq, Syria and Turkey.
They have no official homeland. They are Muslim Sunnis and for centuries have been nomads and fighters.