The sinologist Wing-Fai Leung explained the fantastic origins of the term and the racialist ideology: "The phrase "yellow peril" (sometimes "yellow terror" or "yellow specter") . . . blends Western anxieties about sex, racist fears of the alien Other, and the Spenglerian belief that the West will become outnumbered and enslaved by the East." The academic Gina Marchetti identified the psycho-cultural fear of East Asians as "rooted in medieval fears of Genghis Khan and the Mongol invasions of Europe [1236–1291], the Yellow Peril combines racist terror of alien cultures, sexual anxieties, and the belief that the West will be overpowered and enveloped, by the irresistible, dark, occult forces of the East"; hence, to oppose Japanese imperial militarism, the West expanded the Yellow Peril ideology to include the Japanese people. Moreover, in the late-19th and early-20th centuries, writers developed the Yellow Peril "literary topos" into codified, racialist motifs of narration, especially in stories and novels of ethnic conflict in the genres of invasion literature, colonial adventure, and science fiction.