A world where the Mongols levelled cities as a policy and destroyed Eurasian civilization as a result (Beijing, for example, was burned down by Genghis Khan in 1215). Technological development was retarded worldwide. Eventually, the Black Death drove the Mongols out of Europe, but most of the world is still at a medieval level, with the major centers of world civilization being Japan, West Africa and the Andes. The current year is 2004.
Incidentally, it's called "Attila" because the first scouts to find out mixed up Attila the Hun and Genghis Khan.