The Flemish National Teams come from the European country of Flanders. This is located in present-day Belgium.
Quidditch
The very first ever Quidditch World Cup final took place in 1473, between the European teams of Transylvania and Flanders (QA8, Pm). During this very violent match all 700 known ways of committing a Quidditch foul were recorded (PS11, QA6).
Commentary
Notes
Flanders is located in Northern Belgium. Although it has been playing Quidditch since at least 1473, there is no mention of Quidditch or any other wizarding sport on its Wikipedia entry (Wikipedia).
It is not specified whether the modern teams are still fielded as Flanders or if they have combined with the South of the country and formed Belgian National Teams.
From the Web
Writing by J.K. Rowling on Pottermore:
Pottermore enhanced reading experience: Quidditch World Cup
Screenshots of the original Daily Prophet coverage of the 2014 Quidditch World Cup on Pottermore: Imgur archive
Harry Potter Wiki: Flemish National Quidditch Team
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Tags: brooms / broomsticks cheating dirty first fouls international match Quidditch history sports teams violent Quidditch match