From the 1220s to the 1240s, the Mongols conquered the Turkic states of Volga Bulgaria, Cumania and Iranic state of Alania, and various principalities in Eastern Europe. Following this, they began their invasion into Central Europe by launching a two-pronged invasion of then-fragmented Poland, culminating in the Battle of Legnica (April 9, 1241), and the Kingdom of Hungary, culminating in the Battle of Mohi (April 11, 1241). Invasions were also launched into the Caucasus against the Kingdom of Georgia, the Chechens, the Ingush, and Circassia though they failed to fully subjugate the latter. More invasions were launched in Southeast Europe against Bulgaria, Croatia, and the Latin Empire. The operations were planned by General Subutai (1175–1248) and commanded by Batu Khan (c. 1207–1255) and Kadan (d. c. 1261), two grandsons of Genghis Khan. Their conquests integrated much of Eastern European territory into the empire of the Golden Horde. Warring European princes realized they had to cooperate in the face of a Mongol invasion, so local wars and conflicts were suspended in parts of central Europe, only to be resumed after the Mongols had withdrawn. After the initial invasions, subsequent raids and punitive expeditions continued into the late 13th century.
Melik, one of the princes from the Ögedei family who participated in the expedition, invaded the Transylvania region of the Hungarian kingdom, called Sasutsi in sources.
Composition of Mongolian army
The Mongolian army that invaded Europe in the 13th century (principally the 1236–1242 campaigns led by Batu Khan and Subutai) was highly diverse and ethnically mixed, with ethnic Mongols often comprising a minority of the total force. While the leadership, elite cavalry, and core command in the Tumen units remained Mongol (mainly the Borjigin sub-clan, but also Merkits and Khitans), a significant majority of the soldiers—estimated by some historians to be 70–80% and so the "core army"—were Turkic nomads of the Eurasian Steppe (mainly Cumans/Kipchaks, Bashkirs, Volga Bulgars, Volga Tatars, Kazakhs, and Uyghurs), which were identified in contemporary European sources as "Tatars".
There were also significant numbers of conscripts from conquered sedentary populations, like Chinese people from Northern China, Iranian peoples from Greater Persia, and Caucasians; the Mongol army operationally took soldiers and technology from the peoples they conquered. Chinese specialists, prized due to their expertise in siegecraft, gunpowder, metallurgy and road construction, were primarily kept in the rear echelon operating siege machinery or managing logistics. Some academics have theorized that Mongolian reliance on Chinese and Muslim siege engineers, and their struggles when those non-Mongol specialists were killed or bogged down by European stone fortifications, were more important reasons for the Mongolian withdrawal of Europe than the death of Ögedei Khan.
On the other hand, the Iranians and other Muslims served as the sole bureaucratic, financial, and logistical backbone of the Mongol war machine because Mongols historically despised the tedious work of sedentary administration and urbanization. According to primary sources (like Ata-Malik Juvayni or Rashid al-Din), the Iranians established a network of overseers that was responsible for taking the census, drafting local European men into the infantry (the khashar), and collecting the taxes that funded the westward march. In the end, they settled in the Volga region to manage the empire's western frontier in modern European Russia, being key players in the Islamization of the Golden Horde.
Later, troops from the Russian principalities were recruited after the fall of the Kievan Rus', and were deployed against Poland, Hungary and the HRE during the European advance.
Invasion of Kievan Rus'
In 1223, Mongols routed a near 50,000 army of Kievan Rus' at the Battle of the Kalka River, near modern-day Mariupol, before turning back for nearly a decade.
Ögedei Khan ordered Batu Khan to conquer Rus' in 1235. The main force, headed by Jochi's sons, and their cousins, Möngke Khan and Güyük Khan, arrived at Ryazan in December 1237. Ryazan refused to surrender, and the Mongols sacked it and then stormed Suzdalia. Many Rus' armies were defeated; Grand Prince Yuri was killed on the Sit River (March 4, 1238). Major cities such as Vladimir, Torzhok, and Kozelsk were captured.
Afterward, the Mongols turned their attention to the steppe, crushing the Kipchaks and the Alans, and sacking Crimea. Batu appeared in Kievan Rus' in 1239, sacking Pereyaslavl and Chernigov. The Mongols sacked Kiev on December 6, 1240, destroyed Sutiejsk, and conquered Galicia along with Vladimir-Volynsky. Batu sent a small detachment to probe the Poles before passing on to Central Europe. One column was routed by the Poles while the other defeated the Polish army and returned.
Invasion of Central Europe
The attack on Europe was planned and executed by Subutai, who achieved perhaps his most lasting fame with his victories there. Having devastated the various Russian principalities, he sent spies into Poland and Hungary, and as far as eastern Austria, in preparation for an attack into the heartland of Europe. Having a clear picture of the European kingdoms, he prepared an attack nominally commanded by Batu Khan and two other familial-related princes. Batu Khan, son of Jochi, held supreme command, but Subutai was the strategist and commander in the field, and as such, was present in both the northern and southern campaigns against the Russian principalities. He also commanded the central column that moved against Hungary. While Kadan's northern force won the Battle of Legnica and Güyük's army triumphed in Transylvania, Subutai was waiting for them on the Hungarian plain. The newly reunited army then withdrew to the Sajó river where they inflicted a decisive defeat on King Béla IV of Hungary at the Battle of Mohi. Again, Subutai masterminded the operation, and it would prove one of his greatest victories.
Invasion of Poland
The Mongols invaded Central Europe with three armies. One army defeated an alliance which included forces from fragmented Poland and their allies, led by Henry II the Pious, Duke of Silesia in the Battle of Legnica. A second army crossed the Carpathian Mountains and a third followed the Danube. The armies re-grouped and crushed Hungary in 1241, defeating the Hungarian army at the Battle of Mohi on April 11, 1241. The devastating Mongol invasion killed half of Hungary's population. The armies swept the plains of Hungary over the summer, and in early 1242 regained impetus and launched campaigns into Dalmatia and Moravia. The Great Khan had, however, died in December 1241, and on hearing the news, all the "Princes of the Blood," against Subutai's recommendation, went back to Mongolia to elect the new Khan.
After sacking Kiev, Batu Khan sent a smaller group of troops to Poland, destroying Lublin and defeating an inferior Polish army. Other elements, not part of the main Mongol force, encountered difficulty near the Polish-Halych border.
The Mongols then reached Polaniec on the Czarna Hańcza, where they set up camp. There, the Voivode attacked them with the remaining Cracovian knights, which were few in number, but determined to vanquish the invader or die. Surprise gave the Poles an initial advantage and they managed to kill many Mongol soldiers. When the invaders realized the actual numerical weakness of the Poles, they regrouped, broke through the Polish ranks and defeated them. During the fighting, many Polish prisoners of war found ways to escape and hide in the nearby woods. The Polish defeat was partly influenced by the initially successful Polish knights having been distracted by looting.
Invasion of German lands
On April 9, 1241, Mongol detachments entered the Margravate of Meissen and the March of Lusatia following a decisive Mongol victory at the Battle of Legnica in Poland. The Mongol light reconnaissance units, led by Orda Khan, pillaged through Meissen and burned most of the city of Meissen to the ground. The Chronica sancti Pantaleonis records these attacks.
Invasion of Lands of the Bohemian crown (Bohemia, Moravia)
After the defeat of the European forces at Legnica, the Mongols then continued pillaging throughout Poland's neighboring states, particularly Moravia. King Wenceslaus I of Bohemia returned to protect his kingdom after arriving in Legnica a day late. He gathered reinforcements from Thuringia and Saxony on his way back. He stationed his troops in the mountainous border regions of Bohemia where the Mongols would not be able to utilize their cavalry effectively.
By that time, Mongolian forces had divided into two, one led by Batu and Subutai who were planning to invade Hungary, and another led by Baidar and Kadan who were ravaging their way through Silesia and Moravia. When they arrived to attack Bohemia, the kingdom's defenses discouraged them from attacking and they withdrew to the town of Otmuchów in Poland. A small force of Mongolians did attack the strategically located (on the way to the mountain passes) Bohemian town of Kladsko (Kłodzko) but Wenceslaus' cavalry managed to fend them off. The Mongols then tried to take the town of Olomouc, but Wenceslaus with the aid of Austrian Babenbergs repulsed the raid. A Mongol commander was captured in a sortie near Olomouc. However, due to limited historical data, the Battle of Olomouc at this time is questionable. Under Wenceslaus' leadership during the Mongol invasion, Bohemia remained one of a few central European kingdoms that was never pillaged by the Mongols even though most countries around it such as Poland and Hungary were ravaged. Such was his success that chroniclers sent messages to Emperor Frederick II of his victorious defense. After these failed attempts, Baidar and Kadan continued raiding Moravia (via the Moravian Gate route into the valley of the river Morava towards the Danube) before finally going southward to reunite with Batu and Subutai in Hungary.
Invasion of Hungary
The Hungarians had first learned about the Mongol threat in 1229, when King Andrew II granted asylum to some fleeing Ruthenian nobles (boyars). Some Magyars (Hungarians), left behind during the main migration to the Pannonian basin, still lived on the banks of the upper Volga (it is believed by some that the descendants of this group are the modern-day Bashkirs, although this people now speaks a Turkic language, not Magyar). In 1237 a Dominican friar, Julianus, set off on an expedition to lead them back, and was sent back to King Béla with a letter from Batu Khan. In this letter, Batu called upon the Hungarian king to surrender his kingdom unconditionally to the Tatar forces or face complete destruction. Béla did not reply, and two more messages were later delivered to Hungary. The first, in 1239, was sent by the defeated Cuman tribes, who asked for and received asylum in Hungary. The second was sent in February 1241 by the defeated Polish princes.
Only then did King Béla call upon his magnates to join his army in defense of the country. He also asked the papacy and the Western European rulers for help. Foreign help came in the form of a small knight-detachment under the leadership of Frederick II, Duke of Austria, but it was too small to change the outcome of the campaign. The majority of the Hungarian magnates also did not realize the urgency of the matter. Some may have hoped that a defeat of the royal army would force Béla to discontinue his centralization efforts and thus strengthen their own power.
Although the Mongol danger was real and imminent, Hungary was not prepared to deal with it; in the minds of a people who had lived free from nomadic invasions for the last few hundred years, an invasion seemed impossible, and Hungary was no longer a predominantly soldier population. Only rich nobles were trained as heavy-armored cavalry. The Hungarians had long since forgotten the light-cavalry strategy and tactics of their ancestors, which were similar to those now used by the Mongols. The Hungarian army (some 60,000 on the eve of the Battle of Mohi) was made up of individual knights with tactical knowledge, discipline, and talented commanders. Because his army was not experienced in nomadic warfare, King Béla welcomed the Cuman King Kuthen (also known as Kotony) and his fighters. However, the Cuman invitation proved detrimental to the Hungarians because Batu Khan considered this acceptance of a group he considered rebels as justifications for his invasion of Hungary. After rumors began to circulate in Hungary that the Cumans were agents of the Mongols, some hot-headed Hungarians attacked the Cuman camp and killed Kotony. This led the enraged Cumans to ride south, ravaging the countryside, and slaughtering the unsuspecting Magyar population. The Austrian troops retreated to Austria shortly thereafter to gain more western aid. The Hungarians now stood alone in the defense of their country.