Germany’s war experiences had led, among other things, to a military culture in which the border between civilians and combatants had diminished to a gruesome extent. The fact that during the Franco‐German War German troops had to occupy a large swathe of France, and that the civilians did not behave as foreseen and began resisting the military occupation, was an especially irksome experience.

The myth of ubiquitous francs‐tireurs (free shooters) was born: civilian enemy populations who would shoot at German soldiers, from behind the lines, thereby “stabbing” them in the back. The army decided that, as these people were not enemy soldiers, they could accordingly be treated even more harshly, including by “collective punishment.”⁷

Another worrisome experience in modern Germany’s foundational war was the fact that the Polish population of Prussia—in other words, not civilians of an enemy state but “enemy civilians” within—had behaved in an openly pro‐French manner during the war and that the military command even thought it necessary to keep troops in the Polish regions in case unrest broke out.⁸

The franc‐tireur myth came back with full force in 1914 when Belgium was invaded and occupied; it became the iconic term for enemy civilian populations in war time Germany.⁹ From the beginning of the war, the German military and government were “obsessed” with “the notion of mass civilian resistance.”¹⁰

This spiraled into paranoia and then into violence toward the civilian population of Belgium, which was, for the German army, “a reservoir of potential guerrilla fighters.”¹¹ German papers peddled stories of “Belgian atrocities” committed by civilians against German troops.¹²

(Emphasis added. Source.)