Jack Weatherford in the Los Angeles Times:
Genghis Khan recognized that victory came by conquering people, not land or cities. In contrast to the Americans in 2003, who sought to take the largest cities first in a campaign of shock and awe, the Mongols in 1258 took the smallest settlements first, gradually working toward the capital. Both the Mongols and the Americans used heavy bombardment to topple Baghdad, but whereas the Americans rushed into the capital in a triumphant victory celebration, the Mongols wisely decided not to enter the defeated — but still dangerous — city. They ordered the residents to evacuate, and then they sent in Christian and Muslim allies, who seethed with a variety of resentments against the caliph, to expunge any pockets of resistance and secure the capital. The Americans ended up as occupiers; the Mongols pulled strings, watching from camps in the countryside.
The Mongols also immediately executed the caliph and his sons on charges that they spent too much money on their palaces and not enough defending their nation. They killed most members of the court and administration. The Mongols took no prisoners and allowed no torture, but they executed swiftly and efficiently, including the soldiers of the defeated army who, they believed, would be a constant source of future problems if allowed to live. The first several months of a Mongol invasion were bloody, but once the takeover ended, the bloodshed ended.
By contrast, the American military campaign was quick, with comparatively few Iraqi (or coalition) casualties, but the bloodshed has continued for years. Constrained from decisively dispatching enemies of a new Iraq, the United States has allowed Iraqi terrorists to select who lives and who dies, including women and children, in a slow-motion massacre.