The Trump administration’s announcement that it had decided to open the door to a Turkish invasion of eastern Syria came as a shock to many people. But it shouldn’t have. U.S. policy on Syria has teetered on a thread for more than a year, with many questions about what Washington’s long-term goal was in eastern Syria. While the United States got involved in Syria conflict for a variety of reasons, the central mission that brought U.S. soldiers to eastern Syria has been the defeat of the Islamic State—a goal that was partly accomplished. However, the United States has messages to its partners on the ground and its allies in the region that it has other, often conflicting goals, such as ensuring Turkey’s security and leveraging Syria to reduce Iran’s influence. The decision to withdraw, even partly, after almost eight years of engagement with the Syrian conflict, throws much of that in doubt.

It’s worth looking back at the U.S. role in Syria over the last eight years to understand the complexities involved. The Syrian conflict and America’s role in it is unique but has some antecedents. Washington has sent Americans into a variety of operations with some similar characteristics, such as Operation Enduring Freedom to confront terror in Afghanistan after September 11, or Operation Gothic Serpent in Somalia in 1993, aimed at capturing a warlord. Operation Inherent Resolve’s expansion to Syria began in September 2014 and was aimed at degrading ISIS abilities, especially keeping ISIS from taking the mostly Kurdish city of Kobane on the Turkish border.

The United States was already involved in Syria by the time this operation began. While today’s U.S. role in eastern Syria grew directly from the September 2014 decision to strike at ISIS, leading the United States to partner with local Kurdish forces, the larger picture was more complex. In July 2011, Robert Ford, the U.S. ambassador to Syria, went to Hama where protesters had gathered against the regime of Bashar al-Assad. “He witnessed average Syrians asking for change in their country,” accounts noted at the time. Ford expressed solidarity with protesters, angering the regime. He was pulled out by Washington in October 2011 due to credible threats against him.

The United States decided to help the Syrian rebels. This was supported by then-CIA director David Petraeus and Secretary of State Hillary Clinton, among others. Republicans also supported the program, which saw rebel units vetted and equipped. The initial optimism about the rebels quickly wore thin in 2013 as the groups became more radicalized and foreigners began to be kidnapped in northern Syria. The program would continue but eventually it would be seen as a failure, with assertions that more than $500 million had been “wasted” by 2016. The program was actually larger than that, reaching towards $1 billion by 2017. But U.S. newspapers began reporting in 2015 that only “four or five” of the rebels who were trained were actually fighting, which made observers and policymakers wary of continuing U.S. commitment. U.S. weapons ended up in the hands of other groups besides those they were intended to go to. This was a byproduct of the Syrian rebellion; the opposition to Assad was fractured and preyed upon by extremists. Some of those extremists eventually joined ISIS. The Obama administration appeared to take a “condescending attitude” toward the failure of the program that supported the rebels and became distracted by other issues, such as policies in Asia.

The reality was more than just American fatigue at not being able to find effective allies in Syria to train and equip. Washington was trying to get its global partners to sign onto the Iran Deal in 2014 and 2015 and the Syria rebels were fighting the Iranian-backed Assad regime. Obama had warned the Assad regime in 2012 about crossing a “red line” in Syria using chemical weapons. But in August 2013 the United States failed to act and the “red line” was not enforced. It was clear from that point the United States would not get directly in toppling Assad.

The decision not to strike Assad came despite the State Department’s strong language against his regime. John Kerry, who was secretary of state during the Obama administration, described him as a “thug and a murderer” in August 2013. Kerry also asserted that if the United States did nothing about his use of poison gas then “there will be no end to the test of our resolve and the dangers that will flow.” Kerry would continue to insist that there was no place for Assad in Syria’s future. At this crucial moment the United States began to pursue several different strategies at once, with Kerry involved in the Geneva process discussions about “political transition” in Syria. Inevitably the State Department track would relate to other states that were involved, such as Turkey, Russia and Iran. Turkey opposed the regime, while Russia and Iran supported it. For the United States that would mean NATO ally Turkey was a perfect partner. But a new problem had emerged on the horizon.

Just six months after the decision not to strike the Assad regime, the United States became more concerned about the rise of ISIS. In June, the terrorist organization took over parts of Syria and Mosul in Iraq. That’s about the time that the United States began to support Iraq’s fight against ISIS. By August, when ISIS began a genocide against Yazidis, the Obama administration had expanded its role in the Middle East by conducting airstrikes against ISIS. In September 2014 the United States also opened operations against ISIS in Syria. This  became Operation Inherent Resolve. Eventually the U.S.-led Coalition would come to number more than eighty partners, with only a handful involved in anti-ISIS operations in Syria.

The anti-ISIS track of the U.S. campaign in Syria grew larger in 2015 as the United States began to work directly with the Syrian Democratic Forces, an umbrella group that included elements of the People’s Protection Units or YPG. It was the YPG that had helped defeat ISIS in Kobane and also helped save Yazidis from ISIS. Turkey viewed the YPG as directly linked to the Kurdistan Workers Party (PKK), which the United States and Turkey view as a terrorist organization.

In early 2015, the PKK and Turkey still had a ceasefire. That year, the SDF was founded in October. By this time the YPG had already taken back key areas from ISIS in battles around Tel Tamer, Tel Hamis and Hasakeh. By 2016 the SDF had pushed ISIS out of Tel-Abyad on the border. It was at this juncture that U.S. officials, including Vice President Joe Biden, made clear to the SDF that expanding their victories over the Euphrates River would result in increased tension with Turkey. The SDF crossed the river anyway and liberated the town of Manbij from ISIS. Two elections in Turkey in June and November 2015, as the PKK ceasefire was ending, and a coup attempt in the summer of 2016, fundamentally changed Ankara. Turkish president Recep Tayyip Erdogan emerged stronger and less willing to countenance enemies.

Just a month after the coup attempt, Turkey launched operation Euphrates Shield, a major military offensive into northern Syria in August that replaced ISIS-held areas along the border with a mix of Turkish forces and Turkish-backed Free Syrian Army. Ankara clashed with Washington over claims the United States was not backing Turkey’s expanding role in Syria. It was already clear in at this point in September 2016 that two U.S. policies were on a collision course. A State Department policy working with Turkey and saying one thing and a Pentagon military campaign led by U.S. CENTCOM in eastern Syria. U.S. operations alongside the SDF were expanding in eastern Syria. A token support for some anti-ISIS Syrian rebel fighters, such as those trained at Tanf near the Jordanian border, also continued.

In a revealing article former Secretary of Defense Ash Carter described in 2017 how the United States was fortunate in finding the SDF and “building their combat power,” the way the United States was doing in Iraq with the Iraqi army. “Turkey had been far too slow to respond to the ISIS threat,” and “Turkey was less interested in fighting ISIS than in preventing Kurds in Eastern Syria from linking up with those in the town of Afrin, less than 100 miles from Manbij.” At this point Turkey was still telling the U.S. Arab fighters it backed could take the ISIS capital of Raqqa. “The Turks could never produce an actual plan to field such forces in repeated meetings with the U.S. military,” Carter recalled.

Turkey had hopes that the Trump administration would reverse course on Syria. Instead U.S. anti-ISIS envoy Brett McGurk stayed on and Secretary of Defense James Mattis pushed more U.S. forces into Syria to finish the battle in Raqqa. In the spring of 2017 U.S. special forces and the SDF took Tabqa and eventually liberated Raqqa in October. By this time Turkey was negotiating a deal to buy the S-400 air defense system from Russia, a deal it signed in December 2017. It was also working more closely with Russia and Iran in talks in Astana designed to end the Syrian conflict. Turkish media and Erdogan claimed the United States was training “terrorists” in Syria in January 2018 and Turkey launched an assault on Kurdish YPG forces in Afrin.

The Afrin offensive was a clear sign by Turkey that it would fight the YPG wherever it could find them in Syria if they were not safe under a U.S. air umbrella as they were in eastern Syria. Trump appeared to hint that the United States would leave Syria “very soon” in March 2018. Instead, he appointed John Bolton as national security advisor and brought Mike Pompeo from CIA to run the State Department. Both Pompeo and Bolton wanted to increase pressure on Iran, not only through withdrawing from the deal but via sanctions. Bolton said the United States would remain in Syria until Iran and its forces left the country, potentially using eastern Syria as leverage. That appeared to be U.S. policy until December 19, 2018 when Trump announced on Twitter that the United States would leave. There was no reason to stay, he argued, now that ISIS was defeated. Other should pay for reconstruction and stabilization. This came as news to U.S. CENTCOM, which had not been told that its plans for stabilization and defeating the ISIS remnants were being scratched. Mattis and McGurk resigned. Jim Jeffrey, the special envoy for Syria, had also been left in the dark. Jeffrey would stay on though, taking over McGurk’s role as well