European Union (EU).

The European Union (EU) is a group of countries formed after World War II with the aim of preserving peace in Europe through economic interdependence. While the EU began with just six countries, in 2024 it included twenty-seven full member states. States within the European Union have open borders—passports are not required to pass between them—do not charge duties or tariffs on trade between member states, and charge similar duties and tariffs on trade with non-member states. Most member states have also adopted the "euro," a joint currency. By the mid-2020s, seven EU member states had not adopted the euro. These states—Bulgaria, Czechia, Denmark, Hungary, Poland, Romania, and Sweden—continued to use their own national currencies. Denmark maintains an official opt-out from the euro under EU agreements, while the others have not yet met, or have chosen not to meet, the required convergence criteria for adoption.