sentences:  After an earlier International Union of Directors of Zoological Gardens (IUDZG), founded in 1935 at Basel, Switzerland, ceased to exist during World War II, a new IUDZG was founded in Rotterdam in 1946 by a group of zoo directors from allied or neutral countries.In 1950 IUDZG became an international organisation member of International Union for the Protection of Nature (IUPN), later International Union for Conservation of Nature (IUCN).The IUDZG adopted a new name, World Zoo Organization, in 1991 and revised its membership rules to include regional zoo associations.