One factor was that the Mongols were used to stepped regions suitable for domesticated horses to go across it; so they mostly relied on their horses and east Asia borders to the pacific were full of mountain ranges, and horses were not that good on abrupt terrains.
Another factor was not being experts on shipbuilding either; and although with the help of Korean naval forces they launched amphibious attacks, they mistakenly came during rainy seasons, and the wind blew from mainland to the pacific for several months.
So Typhoons blocked their expansion; plus the heat and humidity levels, another reason for them not being able to withstand.
Typhoons, destroyed most of the invasion fleet, and many soldiers drown before arriving to the shores.
Storms were the most significant factor which Japaneses called “<em>Kamikaze</em>” meaning “divine wind".