Shall we host a world fair is an event, where a heavily industrialised nation can host a World's fair.
It can happen to any great power which has an industrial score over 200 or any civilized nation with an industrial score over 500 in the time period between 1849 and 1935. It will however usually happen much later, as no nation is nowhere near 200 industrial score in 1836. It has a mean time to happen of 800 months (66,6 years), which decrease by 80 % in 1870, 1890 and 1910 (to 640 months, 512 months and 410 months respectively). The event can happen to multiple nations over the course of the game, but never to the same nation twice.
The nation in question has the choice between accepting An Excellent Idea! We Accept!, which costs 1000£ and declining Our ressources would be better used for other purposes., which loses 5 prestige.
Approximately 1 year after the event The World Fair is Opened happens, which gives 22 prestige.
Furthermore if the event happens to 
France it can take the decision Build The Eiffel Tower, which gives additionally 22 prestige (to a total of 44 prestige]]).