World Fairs / World Expos have left a mark since 1851. Which cities have held the most important ones according to Bureau International des Expositions.
The criteria as described on the BIE site: "“World Expos” include all International Registered Exhibitions (2010-present), World Exhibitions (1992-2000), and General Exhibitions of the 1st and 2nd category (1935-1970) organised under the auspices of the BIE, as well as World Expos dating from before the creation of the BIE that are considered of historical importance."
Name the CITIES where the expos were held
Only the most important ones listed as valued by the source, e.g. horticultural expos are not included