The Chinese government (despite its many internal problems) was willing to enter the Great War in order to reclaim concessions lost to Germany and Austria. The Allies were initially hesitant, but as the casualties mounted and the shortage of manpower became acute, Chinese civilian laborers began working behind the front lines. Later, after a U-boat attack killed hundreds of Chinese, China formally entered the war.
Mata Hari earned internationally acclaim as a dancer during the Belle Époque by trading on her exotic (and mostly invented) origins. But during the Great War, being mysterious and not entirely honest can get you killed.