For the next 80 years, Finns and Swedes were inclined to respect Russian security interests, as the Kremlin defined them, even as they joined every Western institution except for NATO—the most binding alliance—and they steered clear of that for two reasons: They knew it would ignite the Kremlin’s paranoia; and they didn’t think they needed NATO’s protection as long as relations with the Kremlin stayed calm.

Putin’s invasion of Ukraine changed all that. It revealed an inflamed paranoia in the Kremlin, and, given the realities of geography alone, it made Finns and Swedes realize they could use some protection after all—especially Article 5 of the North Atlantic Treaty, which obliges members to treat an attack on one as an attack on them all.

The inclusion of Finland and Sweden would also help NATO considerably, bolstering the defenses of Estonia, Latvia, and Lithuania—among the smallest and most vulnerable alliance members—from the north and across the Baltic Sea.

In yet one more way, then, Putin has stirred to life his most dreaded nightmares. Ever since the 1917 Revolution, Soviet (and now Russian) leaders have worried—all of them sincerely, often for good reason—about “encirclement” by their capitalist foes. The invasion of Ukraine reawakened NATO as a military alliance, stiffened its trans-Atlantic ties to the United States, and even compelled Germany to new heights in defense spending. Now with Finland and Sweden about to join as NATO’s 31st and 32nd members, Russia finds itself almost literally encircled—right up to its borders from the south, west, and north.