Baltic escalation goes nuclear.

Yet a series of reports by the nonpartisan RAND Corporation shows that the possibility of nuclear escalation in a conflict between the North Atlantic Treaty Organization and Russia over the Baltic region is higher than one might imagine. The best way of averting it? Invest more in the alliance’s conventional defense.

There was a time when it seemed quite normal to risk nuclear war over the sanctity of European frontiers. During the Cold War, NATO was outnumbered by Warsaw Pact forces, and it would have had great difficulty stopping a Soviet attack with conventional weapons. From the moment it was formed, NATO relied on the threat of nuclear escalation — whether rapid and spasmodic, or gradual and controlled — to maintain deterrence. American thinkers developed elaborate models and theories of deterrence. US and NATO forces regularly carried out exercises simulating the resort to nuclear weapons to make this strategy credible.

After the Cold War ended, the US and its allies had the luxury of thinking less about nuclear deterrence and war-fighting. Tensions with Russia receded and nuclear strategy came to seem like a relic of a bygone era. Yet today, with Russia rising again as a military threat, the grim logic of nuclear statecraft is returning.

The spike in tensions between Russia and the West over the past half-decade has revealed a basic problem: NATO doesn’t have the capability to prevent Russian forces from quickly overrunning Estonia, Latvia and Lithuania. Russian invaders would be at the gates of the Baltic capitals in two to three days; existing NATO forces in the region would be destroyed or swept aside. NATO could respond by mobilizing for a longer war to liberate the Baltic countries, but this would require a bloody, dangerous military campaign. Critically, that campaign would require striking targets — such as air defense systems — located within Russia itself, as well as suppressing Russian artillery, short-range missiles and other capabilities within the Kaliningrad enclave, which is situated behind NATO’s front lines.

Moreover, this sort of NATO counteroffensive is precisely the situation Russian nuclear doctrine seems meant to avert. Russian officials understand that their country would lose a long war against NATO. They are particularly alarmed at the possibility of NATO using its unmatched military capabilities to conduct conventional strikes within Russian borders. So the Kremlin has signaled that it might carry out limited nuclear strikes — perhaps a “demonstration strike” somewhere in the Atlantic, or against NATO forces in the theater — to force the alliance to make peace on Moscow’s terms. This concept is known as “escalate to de-escalate,” and there is a growing body of evidence that the Russians are serious about it.

A NATO-Russia war could thus go nuclear if Russia “escalates” to preserve the gains it has won early in the conflict. It could also go nuclear in a second, if somewhat less likely, way: If the U.S. and NATO initiate their own limited nuclear strikes against Russian forces to prevent Moscow from overrunning the Baltic allies in the first place. And even the limited use of nuclear weapons raises the question of further escalation: Would crossing the nuclear threshold lead, through deliberate choice or miscalculation, to a general nuclear war involving intercontinental ballistic missiles, strategic bombers and apocalyptic destruction?