After World War II, European leaders wanted to remove the economic roots of conflict by managing key industries together. What began with joint control of coal and steel expanded into a customs union and then a common market, officially becoming the EU in 1993. Member states accept shared values such as the rule of law, democracy and respect for human rights, and Europe has enjoyed decades without interstate war. After the Cold War the EU encouraged democratization in Central and Eastern Europe through enlargement, extending a ‘circle of stability’ beyond its original members. Although the Union faces challenges like economic crises and migration pressures, its integration model is often seen as a functional peace-keeping mechanism. The Nobel Peace Prize recognized not just disarmament efforts but the creation of structures that make war among its members almost unthinkable.

European integration has advanced through a step-wise ‘spill-over’ process. The 1951 European Coal and Steel Community placed the core of the war economy under joint supervision, making future conflict economically irrational. The 1957 Treaty of Rome created the EEC, locking market integration into a legal framework. The 1986 Single European Act and the 1992 Maastricht Treaty guaranteed the four freedoms—free movement of goods, people, services and capital—and introduced the euro and the supranational European Central Bank. Throughout the process, accession criteria enforced democracy, minority protection and the rule of law, leading to political convergence among members. Post-Cold-War enlargement used instruments such as PHARE and IPA to transfer institutions and foster democratization and market reform. Statistically, the probability of interstate war within the Union declined as integration deepened. In security affairs, the EU complements NATO but deploys civilian and military missions through the Common Security and Defence Policy to stabilize neighbouring regions.

Within European integration studies, neo-functionalism emphasizes policy spill-over and increasing returns, whereas intergovernmentalism stresses retained state sovereignty. The Nobel Committee viewed integration itself as a peace-building mechanism, effectively raising conflict costs through mutual interdependence and constraining state behaviour via horizontal and vertical legal bindings that mitigate principal-agent problems. Empirically, panel analyses using COW and UCDP/PRIO datasets show near-zero incidence of lethal interstate conflict among EU member states. Negative correlations are observed between single-market depth indicators (trade integration index, FDI stock, regulatory convergence score) and conflict metrics. Through the Copenhagen criteria, institutional diffusion accelerated polyarchization in post-socialist states, significantly improving Fragile State Index scores. Despite contemporary challenges such as democratic backsliding and debates over strategic autonomy, layered governance and reciprocal rule binding continue to suppress escalation to armed confrontation, as evidenced by both quantitative and qualitative studies.