Northern Syria Buffer Zone

The Northern Syria Buffer Zone (also known as the Safe Zone, Peace Corridor, or Security Mechanism) was a temporary Syrian civil war demilitarized zone (DMZ) established on the Syrian side of the Syria–Turkey border in August 2019 to maintain security along the border and to dissuade a prospective Turkish invasion of the self-proclaimed Autonomous Administration of North and East Syria. The DMZ was administered by the Kurdish-led Syrian Democratic Forces (SDF) and their military councils and enforced by United States Armed Forces and Turkish Armed Forces personnel.

The buffer zone collapsed in early October 2019, before it was fully implemented, when Turkey dismissed the agreement on 1 October and the United States abandoned the effort on 6 October after U.S. President Donald Trump ordered the withdrawal of U.S. forces from northern Syria, allowing for Turkish President Recep Tayyip Erdoğan's planned ground incursion into the region. The subsequent Turkish offensive on 9 October rendered the buffer zone fully obsolete.

The failed Turkish-U.S. arrangement was replaced on 22 October 2019 with the separate Second Northern Syria Buffer Zone, negotiated between Russia, Turkey and the Assad government.

The Syrian Democratic Forces are an armed participant in the Syrian civil war and serve as the armed forces of the Autonomous Administration of North and East Syria. The SDF is composed of numerous groups, most prominent among them being the YPG and YPJ and their political branch, the PYD, which Turkey considers a branch of the Kurdistan Workers' Party (PKK), an organization which Turkey considers a terrorist group and with which it has engaged in armed conflict since the breakdown of peace negotiations in 2015. For this reason, Turkey views the entire SDF as merely an extension of the PKK. This has led Turkey to intervene twice against the group by 2019, first by invading northern Syria to prevent the linking of SDF-held areas and later by launching a full-scale attack against the SDF in Afrin. As a result of these incursions, Turkey established an occupation zone in northern Syria, which became subject to an SDF insurgency. Turkish president Recep Tayyip Erdoğan frequently expressed a desire to forcefully remove the SDF from the Syrian-Turkish border.

The SDF, for its part, became one of the United States' main Syrian partners in the war against the Islamic State, leading to US troops being stationed within SDF-held territories, thus dissuading a Turkish cross-border invasion. At the same time, US President Donald Trump expressed his intention to disengage from the Syrian civil war, initially ordering all US personnel in Syria to be withdrawn before later deciding to maintain a small contingent, at the behest of his military advisors. Nonetheless, the US was keen on maintaining good relations with Turkey, which had by that point already been strained by the refusal of the US to extradite Turkish dissident Fethullah Gülen (whom Turkey accused of masterminding the failed 2016 coup d'état) and the Turkish purchase of S-400 missile systems from Russia, as Turkey is considered NATO's key member in the Middle East.

The US and Turkey had previously clashed diplomatically over the issue of the SDF-held city of Manbij, with Turkey wanting to purge the city of the YPG units stationed there. The result was a 'Manbij Roadmap' being agreed to by Turkey and the US, which would eventually entail a YPG withdrawal from the city. The roadmap, however, was never implemented and the YPG never withdrew. Turkey accused the US of dragging its feet and sabotaging the implementation of the roadmap, vowing to never enter into a similar deal in the future.

Relations between Turkey and the SDF became increasingly hostile in mid-2019, with the SDF joining forces with Bashar al-Assad's government forces to repel a Turkish-opposition military operation near Tell Rifaat.

During summer of 2019, Turkish president Recep Tayyip Erdoğan announced that Turkey could "no longer wait" and would not tolerate continued SDF presence along the Turkish-Syrian border. He stated that if the US did not agree to a deal that would remove the SDF from those areas, Turkey would unilaterally launch a full-scale invasion against SDF-held territories east of the Euphrates river, establishing a Turkish-occupied "security zone" along the border – something that US leadership viewed as "unacceptable". With the Turkish army massing along the border, the Trump administration decided to enter into negotiations with Turkey over establishing a "safe zone", which would fundamentally address the SDF presence in Northern Syria. The two sides initially failed to make any headway, with the US initially offering a 10–15 kilometres (6.2–9.3 mi)-deep zone under joint US-Turkish control, while Turkey demanded a 30–50 kilometres (19–31 mi)-deep zone under sole Turkish control.