Complex sentence: He was a former private chief of staff of François Mitterrand, President of the French Republic, from 1989 to 1991, and became chief of defense of the French Armed Forces from 1991 to 1995.
Split into simpler sentences: He was a former private chief of staff of François Mitterrand, president of the French Republic, from 1989 to 1991. He became chief of defense of the French Armed Forces from 1991 to 1995.