“I never fight the same war twice.” ~ a saying attributed to Genghis Khan. The meaning of the saying is that the Mongols used a different strategy in every major battle—that is how they managed to outfox and surprise the military of the nations and cities that they planned to conquer. The Mongols were fast learners. They mastered new techniques of war from the experience of every battle that they fought.
In the early days of Mongol conquests, Genghis Khan realized that his military was finding it difficult to cross rivers and to conquer walled cities and fortified castles. He created a core of engineers for building bridges, catapults, armored siege towers, and other machines of war. The Mongol engineers had the ability to improvise with whatever material was available locally and create a weapon. They often diverted rivers to flood the walled cities and force its rulers to open the city’s gate.
During the siege of Baghdad, which began on January 29, 1258, Hulagu Khan, grandson of Genghis Khan, used an advanced form of gunpowder which produced an explosion instead of fire. The Mongol craftsmen had created tubes that were small enough to be operated by a single soldier. The larger tubes needed more soldiers to operate but could hurl big ceramic balls containing explosive gunpowder mixed with shrapnel. This was a new innovation. The people of the Levant had not encountered the explosive form of gunpowder before.
Hulagu’s army bombarded Baghdad from such distance that they were out of range of the weapons that the city’s defenders had. The city’s rulers and residents were frustrated by the relentless bombardment. The Mongols planted explosives under the walls of Baghdad and created gaps through which their warriors could rush into the city. When the Caliph of Baghdad sent out a force of 20,000 cavalry, the Mongol engineers diverted the river Tigris behind the Arab cavalry, trapping them outside the city and then killing most of them.
After the annihilation of the cavalry, the nobles of Baghdad (about 3000 of them) came out of the city to negotiate with Hulagu but they were slaughtered. Hulagu knew that he was on the verge of conquering Baghdad and so he was not interested in negotiating—he was also following the Mongol policy of sparing most of the common citizens and slaughtering the nobility, because only the nobility had the power to cause rebellions against Mongol rule. The Caliph of Baghdad surrendered on February 10, 1258, thirteen days after the siege began. The Mongols entered the city on February 13.
Halagu established an Ilkhanate whose core territory consisted of Iran, Azerbaijan, and Turkey. At its largest extent, it included parts of modern Iraq, Syria, Armenia, Georgia, Afghanistan, Turkmenistan, Pakistan, part of modern Dagestan, and part of modern Tajikistan. The Ilkhanate lasted till 1335.