Earlier today, Turkey, a NATO ally, shot down a Russian jet, killing at least one pilot, and leaving the other in the hands of insurgents on the ground (and possibly also dead). The Turks claim that the Russian jet was operating in Turkish airspace, and was warned away on numerous occasions. Thus, when its F‑16 fighter jet attacked the Russian SU-24 bomber, it was a legitimate act of self defense. The Turks have called for a NATO meeting later today to explain their side of the story, and, presumably, game out next steps.

Russia claims that its plane was operating over Syrian airspace. It initially reported that it was downed by ground fire, but has since changed its story. Putin is calling it “a stab in the back,” but may stop short of using it as a pretext for substantially widening a conflict he may already regret having been dragged into. There are conflicting reports about whether Russian Foreign Minister Sergey Lavrov has canceled a planned meeting in Turkey tomorrow.

This story bears watching, and I’m reluctant to spin out the historical analogies too far. Very few brush fire wars become world wars, and not all allies behave as the allied and entente powers did in July 1914. Plus, technological changes go a long way to explain why the world today is very different from 100 years ago. I have reason to doubt, for example, that a nuclear-armed Germany would have risked war with a nuclear-armed Russia over Austria-Hungary’s ultimatum to Serbia.

But I nervously tweeted this morning that we might soon appreciate the difference between fighting wars against terrorists and wars against nation-states. We’ve avoided having to think seriously about such things for many years, which may explain the apparent enthusiasm for a no-fly zone over Syria (favored by at least 8 of 11 major presidential candidates). The possibility of Russian jets being shot down, and Russian pilots killed, was dismissed as a hypothetical (Though not by everyone).

It isn’t hypothetical any longer.