sentences:  From the late 19th to the mid-20th century, this was a frequently used and highly controversial tactic employed by the German armed forces to counter the activities of guerrillas behind their front lines.It was used in the Franco-Prussian War of 1870–71 during the German occupation of France, when the Germans were faced with attacks by "francs-tireurs", who were regarded explicitly as unlawful combatants.Mayors of occupied villages were ordered to report "francs-tireurs" operating in their districts or have their houses burned down.