Pundits seeking to predict outcomes in the free-fire zone that is Syria could turn to a 1928 volume called The Command of the Air, by the Italian General Giulio Douhet. Just six years after the Wright brothers’ Kitty Hawk flight, Douhet began thinking about the importance of air supremacy and strategic bombing to winning a future war. In the same way that earlier historians noted the role of seapower in military domination, Douhet saw the atmosphere as a worldwide air ocean...with no hard borders. A decade after The Command of the Air was published, Francisco Franco’s indiscriminate aerial assaults on rebel-held villages during the Spanish Civil War seemed to follow Douhet’s doctrine about terror war waged on civilians, as does Bashar Assad’s attack on “terrorist-held areas” (broadly defined) today.

Now the United States is, with aircraft piloted and unpiloted, asserting itself more boldly in Syria’s part of the air ocean. Until recently the United States limited itself to air strikes in support of American-aligned factions. While chafing at what appeared to be intentional air attacks on Coalition allies by Syrian and later Russian aircraft, the Americans took no action to stop them. Each air force prepared its own mission plans, and each side claimed that its primary goal was destroying ISIS strongholds.

Coalition and Russian air forces in Syria have stayed in touch since 2015 via a “de-confliction channel” that relies on a phone and email link between commands operating in Syria. Recent events, including a shootdown of a Syrian Air Force Su-22 and two Iranian-manufactured weaponized drones to the south, are raising questions as to whether Russian-American tensions will escalate, and how that risk could be reduced. Actual coordination of air strikes in Syria between Americans and Russians isn’t on the table. That’s been prohibited since 2014 by an act of Congress, following Russia’s annexation of Crimea.

The de-confliction channel has been widely publicized, given Russian threats to cut the link after the American cruise missile attack on the Shayrat airfield in March, and again after the Su-22 shootdown. There’s been less attention paid to the Coalition use of another tool, the “de-confliction zone.”

The Coalition has imposed such a dotted line 34 miles around its rebel-training base at Al-Tanf, in the south, which is strategically located near the border conjunction of Syria, Jordan, and Iraq. The Coalition has attacked enemy drones and Syrian-backed ground forces when they approached that boundary. The Coalition’s determination to defend Al-Tanf is a concrete sign of how the Syrian civil war is moving into a new phase, in which ISIS’s diminishing importance is overshadowed by a contest for control of eastern and southern Syria: its cities, resources, and roads. According to the Washington Post, the United States is now keenly interested in the outcome of this contest, as are Iran, Iraq, Russia, the Assad regime, and a jumble of Syrian factions.

If Douhet is any guide, who ends up with what part of the map is likely to depend on control of the skies. So far, so true: Syrian and Russian aircraft have enabled Assad to stay in power during the civil war, but American-led airpower has protected anti-Assad fighters enough to keep his regime in jeopardy.

As of today, no force dominates the skies across all of Syria, and it’s hard to fit peacetime tools to such a novel crisis. Mideast hawks have long argued that the United States should impose a no-fly zone over Syria, but that’s never been tried in such an arena.

The three cases of mandated no-fly zones (Bosnia, Iraq, and Libya) didn’t exist in the face of a modern integrated-air-defense network like that in Syria, nor an active Russian presence.

And there’s little prospect of Russia being able to enforce its own version of a no-fly zone west of the Euphrates River, which it threatened to set up after the American shootdown of the Syrian Su-22.

Setting aside what international law might have to say on the topic, the idea of a smaller, defendable no-fly zone could be attractive. If tensions persist, it’s possible the Coalition will widen its de-confliction zone around Al-Tanf, and create more of what amount to mini-no-fly zones. The Coalition might try to block all Russian and Syrian transits, or could allow controlled, peaceful passage only.

Whether small or large, an emerging weakness of the traditional no-fly zone is the rise of armed drones. Even if a superpower were to declare a no-fly zone over Syria and try to enforce it against conventional aircraft (a risky and costly undertaking), drones are likely to continue flying and shooting, even so. The day will come when drones packing air-to-air missiles take up combat air patrols over previously denied airspace. It’s true that fighter-like, stealthy drones are several years from being fielded, but simulated dogfights between drones and piloted interceptors suggest that they will be…and drones can carry less weight and make tighter turns than piloted aircraft. Aerodynamics aside, many tough questions lay ahead. When satellite, AWACS, and GPS signals are jammed, and victory depends entirely on the drone’s onboard intelligence, can we trust its judgment? Once both sides send out swarms of unpiloted bombers and fighters, how do such engagements play out? Where do they stop?

Depending on the answers to these and other entirely novel questions, it’s possible that drone-on-drone air warfare could be the 21st-century equivalent of the proxy wars so common after World War II, in which superpowers jostled for advantage but only indirectly, by backing small wars around the globe. If the contestants in war zones such as Syria are unwilling to risk piloted aircraft against an opponent’s air defenses, given the public agitation that follows the death an aircrew in combat, drones might be a way to fight for airspace without tipping into a regional, or a world, war.