Chapter 15 offers new perspectives on the formative struggle to establish the League of Nations as an effective international organisation at the heart of the postwar order. It argues that in spite of the global conceptions they advanced its key architects intended the League to become the superstructure of a new transatlantic international order and security architecture. It analyses how far it was possible to find common ground between the most influential American and British blueprints for an integrative League and the markedly different French plans for an institution of the victors whose main purpose was supposed to be to protect France and constrain Germany. And it illuminates why ultimately the League of Nations came to be founded as a truncated organisation dominated by the principal victors of the Great War and initially excluding the vanquished, which were required to undergo a period of probation to become eligible for membership. Finally, it explains the far-reaching consequences this had and examines how far the League nonetheless had the potential to become the essential framework of a modern Atlantic and global order over time.