In 1851, the United Kingdom who was leading the way in terms of industrial innovation, held the very first World's Fair.
Even though the 1855 Paris World's Fair was held 4 years after London 1851, Napoleon III insisted on the fact that France was the first country to have the idea of such an event.
London hosted its second Great Exhibition in 1862 with the aim of surpassing the previous two Expos in size and in scale.
The Paris exposition of 1867, held under Emperor Napoleon III, marked the peak of the Second Empire.