He began his military service in 1869 as a volunteer with the 2nd Life Hussars regiment. During the Franco-Prussian War he was promoted to second lieutenant and recommended for the Iron Cross, Second Class. After an interlude at Halle University, Mackensen formally entered the German Army in 1873, with his old regiment. In 1876 he was promoted to first lieutenant and appointed the General Staff, despite never attending the War Academy.
I. Staff service 1880's II. Ennoblement in 1890's III. WWI IV. Interwar years V. The Third Reich
Very rough article at present