The Pan-Pacific Peace Exhibition was a World's Fair that attracted almost five million visitors to Nagoya, Japan between March and May, 1937. The exhibition was sponsored by the Japanese government, with HIH Prince Higashikuni Naruhiko as chairman.
World's Fair exhibitions were held in many different countries over the years to highlight new developments in science, industry, architecture, and other fields. None of the other fairs had the word 'peace' in the title though, which is particularly sad and ironic in this case. Japan invaded eastern China in what was to become the Sino-Japanese War barely a month after the end of the exhibition. This conflict then merged into the greater World War II conflict.
If you went to the exhibition, you might have stayed at this hotel.
Here's what the back of the postcards look like.