The first World Exposition on Asian soil
Even though Japan had attempted to host a World Exposition at previous occassions in 1912 and 1940 respectively, both of these had to be cancelled - the former due to the death of Emperor Meiji, the latter due to the outbreak of the Second World War. After the 1964 Olympics in Tokyo, which were considered a major success on all levels, it was decided that Japan would host its first World Exposition in Senri in Osaka in 1970. The Osaka Expo was held for a total of 183 days from March 15 to September 13, 1970 and attracted more than 64 million visitors, over 97% of them Japanese
One note: If you are interested in a comprehensive overview over the 1970 Expo pavilions and various other facts about the exposition, I very much recommend this excellent Singaporean site which has more stuff on it than I could ever induldge in (and also great images). Another site with all kinds of facts and photographs is the Earthstation 9 site which is also recommended. If you prefer a printed manual, Minami Nakawada's 2005 "EXPO '70" (published by Diamond Co., Tokyo - available only in Japan ) is an excellent photo collection and good information source.