In the early months of the war in Ukraine, Gen. Mark Milley, then chair of the joint chiefs of staff, carried a note card in his briefcase outlining what he saw as the main priorities when it came to the US and NATO approach to the war. As reported by the Washington Post, they were: No. 1: “Don’t have a kinetic conflict between the U.S. military and NATO with Russia.” No. 2: “Contain war inside the geographical boundaries of Ukraine.” No. 3: “Strengthen and maintain NATO unity.” No. 4: “Empower Ukraine and give them the means to fight.”

The order is telling. Supporting Ukraine has been a priority, but preventing escalation outside of Ukraine has often been a greater one, sometimes to the frustration of Ukrainian leaders who have at times felt that Western governments were too timid in supporting actions like long-range strikes into Russian territory. Milley is long gone from American leadership, but that attitude carried over with the return of President Donald Trump, who has repeatedly expressed concerns that the conflict could escalate to World War III.

So it’s been remarkable over the past week to see the degree to which NATO leaders appear to have come around to the view that NATO-Russia conflict — hopefully only limited conflict — may be inevitable.

The reason is a series of increasingly brazen incursions into NATO airspace. On September 8, 21 Russian drones entered Polish territory, where some of them were shot down by an unprecedented Polish-German-Italian-Dutch military operation.

It’s at least plausible, though somewhat hard to believe given the number of them, that those drones entered Polish airspace inadvertently while on their way to strike targets in Ukraine. Drones have periodically crossed into and crashed on the territory of several NATO countries bordering Ukraine since the start of the war. The fact that they were unmanned vehicles also made the situation easier to deescalate: that drones can be shot down without human casualties is one reason leaders are often willing to take more controversial or riskier actions with them. (In a notable 2023 incident, Russian jets collided with and downed an American MQ-9 Reaper drone over the Black Sea.)

The incident last Friday, in which three Russian fighter jets violated Estonia’s airspace for 12 minutes, where they were intercepted by NATO jets, had the potential to........

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