Cause of death: surgical complications
Joseph Simon Gallieni (24 April 1849 – 27 May 1916) was a French military officer, active for most of his career as a military commander and administrator in the French colonies where he wrote several books on colonial affairs.
He was recalled from retirement at the beginning of the First World War. As Military Governor of Paris he played an important role in the First Battle of the Marne, when Maunoury's Sixth Army, which was under his command, attacked the German west flank. A small portion of its strength was rushed to the front in commandeered Paris taxicabs.
From October 1915 he served as Minister of War, resigning from that post in March 1916 after criticizing the performance of the French Commander-in-Chief, Joseph Joffre (formerly his subordinate, earlier in their careers), during the German attack on Verdun. He died later that year and was made Marshal of France posthumously in 1921.
Source : Wikipedia