After the Second World War, which destroyed 20% of Vienna's buildings, Vienna was divided into four parts. The city was controlled by the allies like the other parts of Austria. In 1955 the state treaty between the allies and Austria was signed in Vienna's Belvedere. After that Vienna became an important city for international organisations. The first was 1957 the International Atomic Energy Organisation (IAEO) and 1965 the OPEC followed. 1980 the Vienna International Center was opened and Vienna is now the third UN-city together with New York and Geneva.