Donald Trump has greenlighted Turkey’s invasion of northeastern Syria in an attempt to remove Kurdish forces from a strip of Syrian land along the Turkish-Syrian border. This decision has prompted outrage and condemnation from politicians on both sides of the political aisle, as well as America’s traditional allies.The Kurdish forces in question were crucial in the fight against Isis, and onlookers fear that Turkey’s military operation will cause yet another humanitarian crisis in Syria. As Turkey’s air force has launched airstrikes, prompting civilians to flee, opponents are scrambling to come up with a way to reverse the Turkish onslaught and protect the Kurds. Some in the region, such as the Kurdish-led Syrian Democratic Forces, have begun to call for the creation of an internationally backed no-fly zone, calls that may only increase after Turkey bombed American Special Forces.No-fly zones, which date back to the first Gulf War, are a physical area in which aircraft are prevented from flying by the airpower of another stronger sovereign state or coalition, and while they often have multiple goals, one is usually to protect vulnerable populations from assault. Their history indicates that no-fly zones have unintended consequences and that keeping them limited to a humanitarian mission is often hard, suggesting that they may not be the best solution for the problems in northeastern Syria today.The first no-fly zones, created over northern and southern Iraq by the George H.W. Bush Administration in the early 1990s, variously served three purposes: civilian protection, containment and a push for regime change.The first of these zones, launched in April 1991 as part of the fallout from the Gulf War, covered territory in northern Iraq above the 36th parallel. Encouraged by Bush, Shia in the south and Kurds in the north had risen up against the Iraqi Government as the war ended. The Bush Administration, however, was wary of fracturing the anti-Iraqi coalition, which had achieved its mission of repelling Iraq from Kuwait, and of inadvertently partitioning Iraq, which enabled Saddam Hussein’s regime to cling to power. This ambivalence allowed Hussein to begin extracting vengeance on the Kurds and the Shia rising up to oppose his rule.The crisis in northern Iraq soon became so acute that Bush was forced to launch a reluctant but successful humanitarian intervention, Operation Provide Comfort, which spawned the April 1991 no-fly zone. Its purpose was initially to defend British and American pilots as they flew aid to Kurdish refugees. But, as the Bush Administration withdrew its ground troops from Iraq, the zone soon took over the role of protecting Kurdish civilians from Hussein. The no-fly zone, policed by regular coalition military patrols, achieved this goal by putting a stop to Hussein’s air force using helicopters against the Kurds, which it had been doing thanks to poor postwar planning.But the no-fly zone was not without unintended geopolitical ramifications. Principal among these was facilitating the emergence of the Kurdistan Regional Government — a de facto Kurdish state in northern Iraq. This development deeply worried America’s ally, Turkey, which feared the separatist impulse among its own Kurdish population. As the base for the aircraft operating the no-fly zone, Turkey’s involvement was key to the operation’s existence, and it often took skilful diplomacy on the part of the Bush Administration to keep the deterrent in place.In August 1992, the Bush Administration created a second no-fly zone, this one over southern Iraq, ostensibly to protect the Shia from Hussein’s continued vengeance.While both no-fly zones were envisioned as short-term measures, each ended up lasting more than a decade as successive US governments struggled to deal with the Hussein regime. The geopolitical cost was often high: the stationing of US troops in Saudi Arabia to run the no-fly zones antagonised powerful forces in the region, including al-Qaeda, helping to precipitate terrorist attacks against the United States.Despite this high cost, little analysis of the no-fly zones took place. Both at the time and in the years since, they have been presented uncritically as straightforward humanitarian interventions. The reality, however, is that no-fly zones were and remain multifaceted tools. Even when they have humanitarian goals, they also have political objectives as well.While the first northern zone furthered humanitarian goals by limiting Hussein’s ability to persecute Kurds, from the beginning, it also allowed the United States and its allies to punish Iraq for its continued refusal to identify and destroy its weapons of mass destruction, despite a United Nations decree ordering that process. The traditional narrative holds that only later, in 1996, did the northern no-fly zone become more about containing Hussein than protecting the Kurds. But in reality the Bush Administration had realised early on that the zone represented a significant impingement on Iraq’s sovereignty and freedom of action.The punitive potential of no-fly zones was expanded by the creation of the no-fly zone over southern Iraq in August 1992. Again dual purposes were at work: Bush and his allies publicly voiced concern about the ever-worsening plight of the Shia, but their main goal was to extract a price for Hussein’s refusal to allow UN-mandated weapons inspections. In fact, the new no-fly zone was meant to be just one part of a wider anti-Hussein operation enacted in August 1992, but the plan’s pièce de résistance, a significant bombing campaign against Iraq, had to be abandoned after damaging leaks from within the State Department embarrassed the Bush Administration.The leaks tied to a third purported purpose of the “renewal of hostilities”, as the Administration called it: domestic politics. Allegedly, the Administration wanted to provoke Iraq into a confrontation timed to coincide with the start of the 1992 Republican National Convention in Houston, Texas. “We are going to stage an incident,” one of the leakers claimed, “to help get the President re-elected”.Without the planned broader campaign, the no-fly zone became the primary new weapon for punishing Hussein. It proved entirely ineffective at protecting the Shia, who faced a significant, ground-based threat. While the northern no-fly zone had protected the Kurds, the geographic and political circumstances were completely different in the south. This difference illuminated how no-fly zones were not a “one-size-fits-all” solution.That has remained true to the present day: since the Iraqi zones were implemented, only two more no-fly zones have been created — each by a US-led Nato coalition — and both produced mixed records. A no-fly zone operated over Bosnia by the Clinton Administration proved ineffective at protecting civilians and a 2011 no-fly zone over Libya, created by the Obama Administration, has proven to be highly controversial. While justified by the Obama Administration on humanitarian grounds, the no-fly zone played a role in the ouster and execution of Libyan leader Colonel Muammar Gaddafi, prompting charges that it was designed to engineer regime change.The sum total of these experiences teaches us that no-fly zones have always had unintended geopolitical consequences. However well-intentioned, a no-fly zone in northeastern Syria could ultimately exacerbate problems in the region or produce repercussions for the West, especially the United States. While stopping Turkey’s attack on the Kurds is a worthwhile goal, a no-fly zone offers more risks than rewards.• Liam O’Brien is a PhD candidate in history at University College Cork and an Irish Research Council Government of Ireland postgraduate scholar