It was only 18 years after last New York World’s Fair. But let us say “a lot had happened.” Wikipedia:

In 1953 Belgium won the bid for the next World's Fair, winning out over other European capitals such as Paris and London.

Nearly 15,000 workers spent three years building the 2 km2 (490 acres) site. Many of the buildings were re-used from the Brussels International Exposition of 1935, which had been held on the same site.

The theme of Expo 58 was “bilan du monde, pour un monde plus humain” (in English: “Evaluation of the world for a more humane world”), a motto inspired by faith in technical and scientific progress, as well as postwar debates over the ethical use of atomic power.

Let's take a look.