Translation:The Kingdom of the Netherlands has different areas.
No, it's 'Nederlanden' because it's plural. It comes from the 'Lage Landen' or 'Nederlanden', a historical region in Europe consisting of current the Netherlands, Belgium, Luxemburg and small parts of Germany and France. See this map:
It is an historical name. See also: https://nl.wikipedia.org/wiki/Koninkrijk_der_Nederlanden