The conclusion offers new perspectives on how after the crises of the 1930s and the even more horrific Second World War a more durable Atlantic order for the “long” 20th century could be created – an order that was founded as a western system led by the new American superpower and rested on the Marshall Plan, the European Recovery Program and the North Atlantic Treaty Organisation. Reappraising the global significance of these developments, it emphasises that what the principal American and west European decision-makers constructed was not just propelled by the escalating cold war with the Soviet Union but rather, on a deeper level, the outgrowth of longer-term learning processes: attempts to draw deeper lessons not only from the rise of National Socialism, authoritarianism and Stalinism and the Second World War but also from the earlier crises and catastrophes of the “long” 20th century, particularly the First World War and the deficient or unfinished efforts to create a modern international system in its aftermath. Finally, it reflects on the challenges of preserving a functioning and legitimate Atlantic and global order in the early 21st century.