In this letter, Batu called upon the Hungarian king to surrender his kingdom unconditionally to the "Tatar" forces or face complete destruction.

[citation needed] The military doctrine of the Hungarian kings prohibited nobles from constructing private stone castles/fortresses for their own protection within the realm.

It was believed that privately built strongholds by landowners could ultimately lead to the strengthening of oligarchy and a decline in the royal power.

Castles were only authorized to be built in strategically significant locations deemed important by the monarchs, primarily along the western border near the Holy Roman Empire.

[16][17] Köten sought asylum in the nearby kingdom of Hungary; the king responded that they could do so as long as the Cumans would convert to Catholicism and acknowledge him as their overlord, providing military service.

Thomas claims that Béla evacuated his wife and daughters along with remains of St Stephen from Szekezfehervar and send them to the littoral parts of the Kingdom.

Defenders hurled rocks on climbing Tatars, kiling several, but the attacks became even fearcer and eventually hand-to-hand combat ensued, and the Mongols started looting the fortress.

[25] However, Rashid Al-Din, a high minister and historian of the Mongol Ilkhanate, specifically states that Batu did not know about Ogedei's death when he decided to withdraw.

He states that they withdrew from Hungary to put down a Cuman rebellion, and then left Europe later in 1242 because they felt they had completed their mission,[non-primary source needed] not because of the influence of any outside force.

Finally, they were stretched thin in the European theater, and were experiencing a rebellion by the Cumans in what is now southern Russia, and the Caucasus (Batu returned to put it down, and spent roughly a year doing so).

[30][failed verification] Another theory relates to Europe's weather: Hungary has a high water table and floods easily.

[33] The combination of massacres perpetrated by the Mongols, the famines induced by their foraging, and the simultaneous devastation of the countryside by the fleeing Cumans resulted in an estimated loss of 15–25% of Hungary's population, some 300,000–500,000 people in total.

[35] However, these places were relatively few; a German chronicler in 1241 noted that Hungary "had almost no city protected by strong walls or fortresses", so the majority of settled areas were extremely vulnerable.

[41] His prediction was ultimately correct, as the Holy Roman Empire (HRE) took little part in fighting the Mongols, bar repelling minor scouting parties in Bohemia, Moravia, Bavaria, and Austria.

A letter written by Emperor Frederick II, found in the Regesta Imperii, dated to June 20, 1241, and intended for all his vassals in Swabia, Austria, and Bohemia, included a number of specific military instructions.

His forces were to avoid engaging the Mongols in field battles, hoard all food stocks in every fortress and stronghold, and arm all possible levies as well as the general populace.

[45] In Bohemia king Wenceslaus I had every castle strengthened and provisioned, as well as providing soldiers and armaments to monasteries in order to turn them into refuges for the civilian population.

There were Mongol raids and sieges in the HRE border states in the aftermath of their victories in Poland and Hungary, in which Frederick's instructions seemed to have been followed, but these were minor affairs and quickly abandoned.

They would be fought over infrequently for the next four years, until the Battle of the Leitha River, where Frederick's death resulted in the counties being ceded to Hungary.

Within a year of the withdrawal of the Mongols, the three westernmost counties (Moson, Sopron, and Vas) that were extorted as ransom by Duke Frederick of Austria were recaptured, and a local uprising in Slavonia was quashed.

[50] The threat of another Mongol invasion, this time taken seriously, was the source of national unity and provided the impetus for Béla IV's extensive expansion of Hungarian defenses, especially the building of new stone castles (forty-four in the first ten years) and the revitalization of the army, including expanding the number of heavily armoured cavalry and knights in the royal army.

Béla IV is seen now as a second founder of the nation, partly in recognition of all that was done during his reign to reconstruct and fortify the country against foreign invasion from the east.