text: A future monarch of this country refused the throne of Greece, believing Greece was too unstable to be a viable monarchy.
full_question: A future monarch of this country refused the throne of Greece, believing Greece was too unstable to be a viable monarchy. That monarch abdicated after his return from exile led to the "Royal Question" and violent strikes in the south of this country. This country's 1830 revolution was sparked by a performance of the opera The Mute Girl of Portici. During World War I, the German Schlieffen plan violated this country's neutrality. The European Union is headed in the capital of this country, which joined two neighbors to form the Benelux union. For 10 points, name this northern European monarchy whose capital is Brussels.
first_sentence: A future monarch of this country refused the throne of Greece, believing Greece was too unstable to be a viable monarchy.
raw_answer: Belgium [or BelgiÃ«; or Belgique]