The term came from a speech by Kaiser Wilhelm II to German troops departing to fight the Boxer Rebellion in China in 1900. The paragraph in question went:

"Should you encounter the enemy, he will be defeated! No quarter will be given! Prisoners will not be taken! Whoever falls into your hands is forfeited. Just as a thousand years ago the Huns under their King Attila made a name for themselves, one that even today makes them seem mighty in history and legend, may the name German be affirmed by you in such a way in China that no Chinese will ever again dare to look cross-eyed at a German."

Wilhelm was known for his bombastic, intemperate pronouncements on foreign policy, and the German Foreign Office found their Kaiser's words ("Go forth and commit war crimes, boys!") so embarrassing that the official publication excised that paragraph. Nevertheless, the term stuck, and Kaiser Wilhelm gifted his country with a derogative that would endure through two world wars.