It is often incorrectly claimed that the European Union is responsible for peace in Europe since Victory in Europe day in 1944. That is not possible as the EU has existed only 26 years being created by the Maastricht Treaty, of November 1, 1993.
NATO and not the EU was responsible for the security of NATO states.
Further the history of Europe has been marred by war and genocide, notably in the Third Balkan war of 1991-2001. In addition to that Greece, Spain, and Portugal were dictatorships as late as the 1970s and Yugoslavia was held together by President Tito's regime until his death.
Additionally, the EU's short history is characterised by the unprecedented social, political and economic instability it has overseen and fostered. President Barak Obama warned against policies like austerity but the EU pressed ahead making money for the banks and increasing poverty, unemployement and unrest in Europe.
So what are the true conditions to foster peace and inhibit war?