A club of European countries. Initially a six-country trade area established by the 1957 Treaty of Rome and known as the European Economic Community, it has become an increasingly political union. In 1999 a single currency, the Euro, was launched in 11 of the then 15 member countries. Viewed as a single entity, the EU has a bigger economy than the United States. In 2002, a further 10 countries were invited to join the EU in 2004, increasing its membership to 25 countries. In January 2007, Romania and Bulgaria became EU members. On July 1, 2013, Croatia became the 28th EU member and more countries are likely to follow later.