A full history of the World Expo
Cities (Bureau International des Expositions).

Starting with just 31 countries the BIE has grown to 170 Member States. These Member States take part in all the decisions of the BIE and their  role is to maintain and improve the quality of all future Expos.

Britain London 1851, France Paris 1889, United States of America San Francisco 1915, United States New York City 1939, Belgium Brussels 1958, United States of America, Seattle 1962, Canada Montreal 1967, Japan Osaka 1970, Brisbane Australia 1988, Spain, Seville 1992, Germany, Hanover 2000, China, Shanghai 2010, Italy Milan 2015, Dubai, United Arab Emirates 2020.

What is the Bureau International des Expositions?

The BIE is the Organization in charge of overseeing and regulating all international exhibitions known as Expos.

The following are the 4 four types of Expos: World Expos, Specialised Expos, Horticultural Expos and the Triennale di Milano.

The BIE Expos organization is set-up to ensure the standards and the success of these world events. Their primary role is to protect the rights of the organizers and participants. Their secondary role is to ensure their core values of Education, Innovation and Cooperation is upheld. The chosen host nation is provided with expertise in event management, national branding and public diplomacy.

Regulating the organization

The BIE is also responsible for making sure the host country and all participants follow the convention of the BIE and the guidelines set out for all past, present and future Expos.

Sources:
https://www.bie-paris.org/site/en/component/content/article?id=191&Itemid=598