In 2014, Russia invaded and annexed Crimea, upending the European security architecture. After that, says Marten, Sweden and Finland began working more closely with NATO. In that sense, “it’s been a gradual increase; this [application announcement] just makes it official,” she says. “It’s confirmation of the direction they were along.” February’s invasion merely clarified the stakes, particularly as Russian troops have reportedly engaged in massacres in Ukraine.
See also Marten’s article in Foreign Affairs (May 4, 2022).