There are people capable of changing the world. One of these was Temujin, who brought the scattered Mongol tribes together under his power. In the early thirteenth century, under the name of Genghis Khan, he subdued entire nations. The Mongol army, reformed by Genghis Khan, crushed Mongolia's neighbors and was later victorious over China. In 1217, the Mongols headed for the vast Khwarezmid Empire, and gained full control over it by 1225. Throughout this period, Genghis Khan's army was improving its skills and refining its tactics, borrowing military achievements from conquered states.

After the conquest of Khwarezmia, Genghis Khan sent Jebe and Subutai, his best military leaders, to scout lands in the west. These master tacticians of the steppes carried out a probing action, leading their battalions through the Caucasus and the lower straits of Don River to Crimea. During this battle march, they drove Kipchaks, former steppe masters, away towards the Dnieper. In spring 1223, Kipchak Khan Kotyan asked his son-in-law, Mstislav the Bold of Halych, for help. Mstislav agreed to provide it, and in late May 1223 Mongols saw the united forces of many Russian principalities and Kipchaks on River Kalka. The Mongols were outnumbered, but Subutai and Jebe did not like to lose. They accepted the battle.
It became clear after the Battle of Kalka River that the steppe now had new masters. The Mongols returned to their endless domains, but those who thought it would be forever made a bitter mistake.

Long before his death in 1227, Genghis Khan divided his huge state among his heirs, giving each of them a khanate reporting to the Great Khan. The khanate of Jochi, Genghis Khan's elder son, and that of his successors, stretched from the Siberian rivers of Irtysh and Chulym to the west "as far as horse hooves can ride." Batu, Jochi's son and Genghis Khan's grandson, drove his horses beyond Volga River towards Kievan Rus' in 1237.

Russian principalities offered valiant resistance, but in general, they were not ready to face the Mongols. Forces of Prince Yury Vsevolodovich of Vladimir and Suzdal were unprepared for the engagement with Batu Khan's advanced units on the Sit River on a morning in March 1238. This was one of many battles between 1238 and 1240 that reaffirmed the Mongols' influence over Kievan Rus'. Having crossed all of Rus', and having reached its western borders, Batu divided his army into several corps and decided to move further to Poland and Hungary.

The invasion began with Poland. The corps of Baidar, Batu Khan's cousin, seized the largest Polish cities, including Lublin, Sandomierz, and Krakow, in just one month, destroying any Polish detachments that tried to halt its advance. Count Henry of Silesia blocked Baidar's corps with a large force of Polish and European knights at Legnica in early April 1241.
After this battle, many people attributed Mongolian victories to craftiness or sorcery. But it was not supernatural forces that helped Mongols; a highly disciplined and mobile army was trampling Poland, and none could overcome its new tactics.

The route to Hungary ran across the Carpathian Mountains, and through the snow-covered Veretski pass. King Bela IV of Hungary ordered the placement of abatis in the pass, and placed a powerful barraging detachment behind it. But Batu Khan's army made its way through the abatis and defeated the enemy in mid-March 1241. The way to the Hungarian plains was clear.
Bela IV gathered his army in the capital city of Pest and prepared for defense. But besieging a reinforced capital with a powerful garrison would prove costly for Batu Khan, and so he commenced a slow retreat, hoping to lure the enemy from the fortress. Bela IV rose to the bait, and gave chase to the Mongols. In early April 1241, it seemed to him that he had deadlocked them with their backs to the Sojo River amidst the spring flood.
The Hungarian army was large, and the Hungarian cavalry was famous all over Europe. But what happened on a Sojo bank made the King of Hungary flee, and the name Tatars, which Europeans used in reference to Mongols, inspired awe throughout the whole continent from that moment on.

The Mongol army reached Adriatic shores in 1242, but in March, Batu received news of Ogedei Khan's death. In brief, this news saved Europe. Batu was obliged to return to take part in the elections of a new Great Khan. The Mongol army, now bearing a resemblance to a long snake, began to retreat towards the east, leaving forever. Europe would face such a powerful adversary again centuries later.