The collection of correspondence of Hüseyin Hilmi Pasha, who was the Grand Vizier at the time of the March 31st Incident, is an important source for researchers interested in late Ottoman history, the Committee of Union and Progress, the Balkans and Macedonia. Hüseyin Hilmi Pasha's official and personal correspondence is an important primary source for national and international political developments in the Balkans, especially during his Rumelia Inspectorate. The documents from this inspectorate period account for more than half of the collection.