Europe’s security environment was fundamentally altered by Russia’s invasion of Ukraine which gave fresh impetus to states to apply for NATO membership. This book, written by leading experts on European defence, analyses NATO’s northern expansion, detailing the unique dynamics that forged Finland and Sweden’s path to NATO membership. The book uses resources in Swedish, Finnish and English to offer a balanced study of both political and military aspects of NATO enlargement. Exploring the pressing issues that NATO will need to tackle, particularly in Northern Europe, the book considers the potential repercussions the newest round of NATO enlargement will have on European and global security.