Feigned retreat seems to have worked on nomads as well as most others.

Both the Vietnamese and the Japanese saw off excessive Mongol (well, more like Yuan China but anyway) ambitions in their directions, but let's be honest - they were getting some serious flank support from General Geography. The terrain in Vietnam alone must have robbed the invaders from most of their usual strong points, and in Japan... well, the Yuan weren't exactly amphibious assault specialists, or terribly good seafarers for that matter.