No-fly zones aren’t as easy as they sound. Chris Chivvis, a former US intelligence official who works for the Carnegie Endowment, explains:

I share the frustration over Putin’s murderous war. Pressure is growing for a no-fly zone (NFZ) over Ukraine. But I fear we have grown accustomed to fighting enemies who had no way to out-escalate us.

[We can learn about] our options and the risks of escalation [from the history of no-fly zones]:

Eleven years ago, the U.S. was on the cusp of imposing its no-fly zone over Libya to stop Qaddafi’s attacks on civilians. NATO expected a quick no-fly zone operation in Libya. Conditions were favorable because most of Qaddafi’s air force had defected.

But the Libyan dictator still had old Soviet long-range surface to air systems — SA-2 Guideline, SA-3 Goa, and SA-5 Gammons. NATO had to destroy these threats for its planes to fly safely.

And so, the US and UK fired 130 Tomahawk cruise missiles, US B-2 Stealth Bombers dropped 45 precision-guided bombs on Libya, and other NATO aircraft attacked across the country.

What would this look like in Ukraine eleven years later? Russia isn’t Libya, so naturally, the military requirements would be much more stressing. And escalatory.

Consider the reports that Russia has deployed several air defense systems to the theater, including S-400s, their most advanced. These would have to be eliminated for NATO pilots to fly safely over key parts of Ukraine, including potentially Kiev. This means NATO — and almost certainly US pilots — would have to bomb Russian units outside of Ukraine (e.g. S-400s in Belarus). They would also have to engage Russian planes flying over Ukraine. Russia could attack them from within Russian and Belarussian airspace. Would our pilots be allowed to return fire? If so, NATO would then be attacking Russians inside Russia. If not, some US pilots would probably be shot down.

The pressure to broaden the war would then become insurmountable. Unfortunately, there’s an even easier way a #NFZ would escalate. . . 

NATO would struggle to fly passively over Ukraine’s cities while Russia showered them with cluster munitions. We would probably end up attacking Russian forces on the ground [in Ukraine]. That’s not a risk I’m ready for. 

Meanwhile, the historical precedents of NATO NFZs would almost certainly encourage Putin to escalate. Libya is one precedent Russians often complain about, but the 1999 Kosovo air campaign is no less important for several reasons.

In 1999, the United States began an air campaign against Serb forces who were killing Kosovars. Many experts at the time expected the nationalist Serb leader Slobodan Milosevic would capitulate after only a few days. Did he? No. Everyone was surprised when the operation dragged on for months – just like in Libya. Eventually NATO widened its strikes to include civilian infrastructure in Serbia itself. Milosevic capitulated and within a few years was overthrown – just like Qaddafi.

Putin almost certainly has both Qaddafi and Milosevic – and obviously Saddam Hussein – in mind when he looks at Ukraine today. But unlike these despots, the one in the Kremlin has many options for escalation. Anyone who thinks he won’t use them isn’t watching the news.