The major event that led to the formation of the European Union (EU) was the Treaty of Maastricht, signed in 1992. Initially building on earlier European integration efforts, such as the European Economic Community established in the 1950s, the Maastricht Treaty formalized the EU as a political and economic entity. It introduced the concept of European citizenship and laid the groundwork for the euro, promoting economic stability and cooperation among member states. The EU aimed to foster peace, security, and economic integration in Europe, transforming the continent into a more unified entity in the post-World War II era.