The Visegrád Group (also known as the Visegrád Four, the V4, or the European Quartet) is a cultural and political alliance of four Central European countries: the Czech Republic, Hungary, Poland, and Slovakia. The alliance aims to advance co-operation in military, economic, cultural and energy affairs, and to further their integration with the EU. All four states are also members of the European Union (EU), the North Atlantic Treaty Organization (NATO), and the Bucharest Nine (B9). The alliance traces its origins to the summit meetings of leaders of Czechoslovakia, Hungary and Poland, held in the Hungarian castle town of Visegrád on 15 February 1991. Visegrád was chosen as the location for the summits as an intentional allusion to the medieval Congress of Visegrád between John I of Bohemia, Charles I of Hungary, and Casimir III of Poland in 1335. After the dissolution of Czechoslovakia in 1993, the Czech Republic and Slovakia became independent members of the alliance, incrementing the number of members from three to four. All four members of the Visegrád Group joined the European Union on 1 May 2004. Historical background The name of the group is derived from the place of meeting selected by the 1335 Congress of Visegrád held by the Bohemian (Czech), Polish, and Hungarian rulers in Visegrád. Charles I of Hungary, Casimir III of Poland, and John I of Bohemia agreed to create new commercial routes to bypass the city of Vienna, a staple port, which required goods to be offloaded and offered for sale in the city before they could be sold elsewhere, and to obtain easier access to other European markets. The recognition of Czech sovereignty over the Duchy of Silesia was also confirmed. The second Congress took place in 1339 and decided that if Casimir III of Poland died without a son, which actually happened, the King of Poland would be the son of Charles I of Hungary, Louis I of Hungary. From the 16th century, large parts of the present-day territories of the group's members became part of or were influenced by the Vienna-based Habsburg monarchy until the end of World War I and the dissolution of the Habsburg-ruled Austria-Hungary. After World War II, the countries became satellite states of the Soviet Union, as the Polish People's Republic, the Hungarian People's Republic and the Czechoslovak Socialist Republic. In 1989, the fall of the Berlin Wall and the fall of communism