For almost half a century, NATO and the Soviet-backed Warsaw Pact alliance glowered at each other from across the Iron Curtain. But after the USSR collapsed, NATO expanded eastward by welcoming former Eastern Bloc members – a development Moscow viewed as a direct challenge to its sphere of influence.
This dynamic has again been a massive point of contention since Moscow unleashed a war against Ukraine, causing states like Finland and Sweden to submit hurried bids to join the defense alliance. Finland joined in the spring. And this week, Turkey's President Recep Tayyip Erdogan, who had been holding up Sweden's bid, finally gave Stockholm the green light. Here's a look at the history of the alliance's expansion.
