"Professor Binns had asked for a three foot-long composition on 'The Medieval Assembly of European Wizards'."
-- CS9
The Medieval Assembly of European Wizards was a medieval society across Europe. Professors Binns assigned a three foot-long composition on “The Medieval Assembly of European Wizards” in Harry Potter’s second year. Ron Weasley’s essay was eight inches short, while Hermione had written four feet seven inches in tiny writing.
On the old Pottermore, the Medieval Assembly of European Wizards' homework scroll. It sat on on Dean Thomas' desk, to the right of Hermione's, next to the window.
Commentary
Notes
This appears to be the Wizarding World's closest equivalent to the European Union. However we have no evidence to suggest that the Assembly still exists in the present day. It should be noted that in the movie universe this organsation still exists, but that is not cannon. -ibid
From the Web
The Medieval Assembly of European Wizards from the Harry Potter wiki
Does the Wizarding World have a European Union? from Scifi Stackexchange