Celtomania

Celtomania is the name given to the rise in popularity of Celtic literature and culture in the early nineteenth century. Important causes of this popularity were James Macpherson's publication of the Ossian poems, and sublime descriptions of Celtic landscape such as found in the works of Jacques Cambry. Celtomania in France was strengthened by Napoleon's idea that the "French were a race of empire-building Celts," and became institutionalized by the foundation of the Académie Celtique in 1805, by Cambry and others. Excesses were to be found in the work of many, including Charles Mackay, who was criticized by his contemporaries already for his fanciful etymologies (dubbed "Celtomaniac absurdities").

...
Wikipedia