The Ottoman army remained very powerful in the open field but it often lost a significant amount of time besieging the many fortresses of the Hungarian frontier and its communication lines were now dangerously overstretched.

[5] Ferdinand, under pressure from the local nobility, decided to respond by launching an offensive in Slavonia in 1537, sending one of his ablest generals[4] to take Osijek.

The siege failed and led to the Battle of Gorjani, which was a disaster as big as Mohács, with an Ottoman relief army smashing the Austrians.

The troops were withdrawn from Italy after an expected French invasion designed to coordinate with Ottoman efforts failed to materialize.

[13] In fact, the Holy Roman Emperor Charles V sent Spanish troops to help his brother regularly from 1527 to 1553, support that proved instrumental in Hungary remaining inside Christianity.

[14] In the spring of 1551, the Ottomans held the Hungarian border forts of Pécs, Fehérvár, Esztergom, Vác, Nógrád, Hatvan and Szeged.

György Fráter deceived the sultan - in fact, he only wanted to gain time and finally hand over Transylvania, which had been under the rule of the Kingdom of Hungary since 1003, to the Hungarian king, Ferdinand of Habsburg.

The commander-in-chief of his army, Kara Ahmed, who left Constantinople, was the serdar[general] and other commanders were Mehmed Sokollu beglerbey of Rumelia and Hadim Ali pasha r(governor) of Buda.

Ahmed's army's aim was to acquire the Timisoara region, while Hadim Ali had to occupy the castles of Hont and Nógrád, thus securing the way to the rich mining towns of the highlands.

During the campaign they occupied Timișoara, Veszprém, Szécsény, Hollókő, Buják, Lippa, Lugos, Karánsebes, Drégely and several smaller fortresses.

In 1552, Suleiman's united forces (Kara Ahmed pasha, Hadim Ali pasha, and Mehmed Sokollu beglerbey) laid siege of Eger, located in the northern part of the Kingdom of Hungary, but the defenders led by István Dobó repelled the attacks and defended the Eger Castle.

In 1554, the town of Fiľakovo in south-central Slovakia with the castle of the same name was conquered by the Turks and was the seat of a sanjak until 1593, when it was reconquered by the Imperial troops.

On 27 March 1562, Hasszán, the sanjak-bey of Fülek (Fiľakovo) castle, defeated the Hungarian army of the Upper Lands at the battle of Szécsény [sk].

After the Turkish attack, led by Toygun Paşa, governor of Buda, was repulsed by László Kerecsényi in 1555,[16] the first full-scale siege of the fortress took place in the summer of 1556.

Despite the extraordinary efforts of the Ottomans the castellan in charge of the defense, Marko Horvat Stančić [hr],[17] kept the fortress against the multiple attacks led by Ali Pasha, governor of Buda.

He was tasked with maintaining the last important southern border fortress, still in imperial hands, endangering the security of the military and commercial road between Buda and Nándorfehérvár.

He besieged the castle of Szigetvár with an army of hundred thousand regular forces,[19][20] which Zrinski defended with about 2,500 soldiers, resisting the Turkish superiority for 34 days.

No large armies or sustained campaigns were launched, but authorities on both sides continually struggled with hostile raiders and forays across the poorly-demarcated border.