The causes of the First World War remain a central preoccupation for international relations scholars. Some find them in the actions of particular aggressors, others in the logic of zero-sum competition between bipolar alliance blocs. Still others describe how an ever more mechanical European state system became increasingly inflexible until it seized up and exploded. I turn this perennial query on its head, asking not why war erupted in 1914, but how Europe’s political class was able to avoid wars during the thirty-three years of pan-Great Power peace stretching from the Berlin Congress (1878) to the Italo-Turkish War (1911).

I argue that the Berlin Congress founded an international regime, which, like its predecessor founded at the Congress of Vienna (1814-15), was framed as a “Concert of Europe,” and was predicated not on a balance of power but on normative principles of international relations, chief among them being the inviolability of member state territorial integrity and sovereignty. Like its Vienna predecessor, this Second Concert recognized subordinate principles, namely minority protections, national self-determination, and human rights. By surveying reportage on the Concert during the regime-challenging crises these subordinate, and state-challenging, principles instigated, I show how the Concert-loyalty of the regime’s member states led to affirmations of the supremacy of the territorial state, thereby preserving both the Concert regime and general peace. This era of tranquility ended with the Bosnian Crisis (1908-09), which saw the first violation of Concert principles by one of its members since the regime’s founding, resulting in the Concert’s dissolution. Europe, plunged back into an international state of nature in which power alone ruled, experienced rapidly escalating violence that culminated in general war.