The Mongol invasion of Khwarezmia, which lasts from 1219 to 1221, marks the beginning of the Mongol Conquest of the Islamic States, and it also expands the Mongol invasions, which will ultimately culminate in the conquest of virtually the entire known world, save for Western Europe, Fennoscandia, the Byzantine Empire, Arabia, Africa, Indian subcontinent, Japan and parts of Southeast Asia.Ironically, it had not originally been the intention of the Mongol Khanate to invade the Khwarezmid Empire.

Indeed, Genghis Khan had originally sent the ruler of the Khwarezmid Empire, Ala ad-Din Muhammad , a message greeting him as his equal: "you rule the rising sun and I the setting sun."

The Mongols' original unification of all "people in felt tents", unifying the nomadic tribes in Mongolia and then the Turkmens and other nomadic peoples, had come with relatively little bloodshed, and almost no material loss.

Even his invasions of China, to this point, have involved no more bloodshed than previous nomadic invasions had caused.

It is the invasion and utter destruction and complete devastation of the Khwarezmid Empire which earns the Mongols the name for bloodthirsty ferocity that will mark the remainder of their campaigns.

In this brief war, lasting less than two years, not only is a huge empire destroyed utterly, but Genghis Khan introduces the world to tactics that will not be seen again until the Germans use them so well in the Second World World War - indirect attack, and the complete and utter terrorization and wholesale slaughter of entire populations.