Army group

Army groups appeared once fronts grew so long that a high command could no longer direct a dozen or more armies directly. The French set up the first, a provisional northern army group, as early as October 1914; Army Groups North, East and Centre followed in 1915. German army groups were named after their commanders, such as Mackensen's, which broke through at Gorlice in 1915 and then attacked Serbia, or those of the crown princes, Rupprecht of Bavaria and Wilhelm of Germany, in the west. An army group commander often led one of its armies at the same time.

Army groups should be distinguished from the smaller ad hoc groups of a few corps named after their commanders, such as General von Fabeck's group at Ypres in 1914. In 1918 the Flanders Army Group was also formed under King Albert I of the Belgians.