Poland, the Czech Republic, the Slovak Republic, and Hungary are members of the Visegrad Group, created in February 1991 at the northern Hungarian town of Visegrad. After World War II until 1989-1990, these countries were Communist states, as Well as members of the Warsaw Pact. On January 1, 1993, the Czech and Slovak Republics, previously Czechoslovakia, split to form two separate states. During the past decade, the Visegrad group has made the transition to democracy and to market-based economies. On May 1, 2004, the Visegrad countries became members of the European Union (EU). In 1999, Hungary, Poland, and the Czech Republic became the first former Warsaw Pact countries to join the North Atlantic Treaty Organization. Slovakia joined NATO in 2004. The Czech Republic became a member of the Organization for Economic Co-operation and Development (OECD) in 1995, Hungary and Poland joined in 1996, and Slovakia in 2001. As members of the Visegrad Group, the four countries also belong to Central European Free Trade Agreement (CEFTA). Slovenia, Romania, and Bulgaria are members too. The Visegrad countries are dependent on trade with the EU, in particular with Germany. These four countries also continue to face economic restructuring challenges, including: modernizing large, and to a certain extent, antiquated agricultural sectors implementing more energy efficient processes for industry in order to decrease energy consumption; absorbing the costs from cleaning up heavily-polluting industries; and adapting industries and services to EU standards.