The Mongol invasion of Kievan Rus began in the 1220s and lasted a relatively short time. The last city of Kiev fell under Mongol rule in 1240. After that, the Mongols turned to what had been their goal before, and that was the conquest of the rest of Europe.
After these events, the Mongols split into three armies and prepared for war against Poland and Hungary. Near the town of Liegnitz on April 9, 1241. they were greeted by an army of 20,000 Teutonic knights. These knights were completely unprepared and unfamiliar with the warrior skills nurtured by the Mongols, and in that battle most of them were killed. Meanwhile, another Mongol army conquered Krakow. The whole of Poland was badly damaged in the raids.
The third Mongol army was the one under the command of Batu Khan. This army penetrated from the territory of today’s Ukraine into the Hungarian Transylvania (modern Romania), and struck the first blows at the Hungarian outposts there. In the spring of 1241, the Mongols had already advanced through the territory of present-day Hungary. King Bela IV. he set out to meet them with 65,000 soldiers (mostly peasants and commoners gathered in a hurry). The Mongols encamped on the river Sajo in the Mohi wasteland near the present-day town of Miskolc.
To help Bela IV. his brother Colloman, who was the Croatian herceg (viceroy of Croatia), arrived. He led a strong army composed of Croat infantry and cavalry. On the Hungarian-Croatian side, Archbishop Ugrin and his fighters participated as one of the military leaders, as well as the Grand Master of the Templar Order with his knights. The Hungarian-Croatian army encamped near the bridge over the river Sajo. King Bela and herceg Koloman were not experienced military leaders and formed a cramped camp of a defensive character surrounded by chariots. In such cramped conditions, the soldiers disturbed each other in the crowd and no strategic attack could be undertaken from such a camp. In the event of a failure on one wing or in the center, there must have been confusion at the other end of the battlefield as well. Batu Khan, who had already successfully defeated the Russians and Poles, watched the camp from a mound and confidently announced to his superiors that no one would escape from it alive.
The bridge over the river Sajo was guarded by a thousand soldiers by the king’s order. When the Mongols tried to break through, his defenders were joined by herceg Colloman and Croatian troops united with the forces of Archbishop Ugrin. Although some Mongols had already crossed the river the defenders drove them back. Enthusiastic Colloman hurried to announce his victory to his brother Bela, but the same night after they pelted the bridge with stones in battle machines, the Mongols crossed the river. What over the bridge, what about horses downstream from it.
At dawn the next day, the Hungarian camp was surrounded by Mongols arranged in a horseshoe shape. The Christian army was showered with a real rain of arrows, the chaos was complete, and few more listened to the commanders. At one point the flames engulfed all the tents, the arrow was more and more, and the chaos turned into panic. herceg Colloman’s troops, together with those of Archbishop Ugrin and the Templars, tried to make a breakthrough, but without success. Ugrin and the Grand Master of the Templars were killed in an attempt to break through, and Colloman was severely wounded.
The soldiers fled, and the result of the battle was more than catastrophic. Of the 65,000 soldiers of the Christian army, 50,000 remained on the battlefield. Colloman managed to escape to Croatia via Buda, but he died of his wounds in Čazma the same year. Having won on the Sajo River, the Mongols massacred a large number of the inhabitants of Hungary, and the few survivors escaped by fleeing into the woods and up. Waiting for the harvest, they continued to penetrate to the south, at the same time persecuting King Bela, who fled to Croatia via Austria. Bela IV. asked for help from other European rulers, but no one responded. In February 1242, the Mongols crossed the Danube and the Drava, and looted Croatia. Bela retreated to Dalmatia in front of them and took refuge in the fortified cities of Klis, Split and Trogir, which the Mongols failed to capture. During the siege of Trogir, Bela took refuge on the nearby Dalmatian islands. Then, in March, news arrived of the death of the great Khan Ogotay, and Mongol troops under Batu Khan and Kadan returned to Asia, ravaging and burning in Bosnia, Serbia, Bulgaria, and southern Russia.
After the end of the war threat, the king returned to Hungary. The state was ravaged and devastated, the state organization weakened, and after the departure of the Mongols famine and plague reigned. For the better defense of the kingdom, King Bela IV. he began to build fortified cities, and he encouraged ecclesiastical and secular nobles to build them. To revive the desolate country, he encouraged the immigration of foreigners, especially Germans, to whom he distributed privileges. Thus begins the accelerated development of cities. Some of them became „free royal cities“ by royal privileges, and were given the right to choose their own administration.