NATO did dramatically enhance the independence and prospects of Montenegro. On the day NATO’s invitation was announced, my Montenegrin colleague in Vienna was grinning widely. She had helped negotiate Montenegro’s independence a decade earlier, and as she hugged me she declared, “It’s as if a weight that has been on my shoulders forever, for my whole life, has been lifted.”

And then I realized: The reason the Russians cared so much about blocking NATO membership is that they knew it would reduce their ability to manipulate Montenegro and would remove a chess piece from a board on which they sought to challenge Europe. Indeed, in the months after NATO’s invitation, Russia continued its attempts to stymie Montenegro’s path by stirring up internal unrest through propaganda, paid protesters and even an attempted coup. They failed.