It's taken nearly two years of political jousting and a war of words with multiple member states - not to mention a series of menacing threats from Vladimir Putin. 

But Sweden has now formally joined NATO in what constitutes a stunning break with a two-century-long policy of military neutrality. 

Prompted by the Russian invasion of Ukraine in February 2022, the Scandinavian nation and its Nordic partner Finland conducted a comprehensive review of its longstanding national security policy and just two months later applied to join the mammoth bloc.