Complex sentence: The Congress of Vienna formed Luxembourg as a Grand Duchy within the German Confederation in personal union with the Netherlands, while at the same time ruled as a province of the Netherlands, with a Confederate fortress manned by Prussian troops.
Split into simpler sentences: The Congress of Vienna formed Luxembourg as a Grand Duchy in personal union with the Netherlands. Luxembourg also became a member of the German Confederation, with a Confederate fortress manned by Prussian troops.