he loss of Belgrade (Nandorfehervar) in 1521 caused great alarm in Hungary, but the too-late and too-slowly-recruited 60,000 strong royal army – led by the king - forgot to take food along, so therefore the army disbanded spontaneously under the pressure of hunger and disease without even trying to recapture Belgrade, the southern key of Hungary, from the newly installed Turkish garrisons. In 1523, Archbishop Pál Tomori, a valiant priest-soldier, was made Captain of Southern Hungary. The general apathy that had characterized the country forced him to lean on his own bishopric revenues when he started to repair and reinforce the second line of Hungary's border defense system.
Three years later, an Ottoman army set out from Istanbul on 16 April 1526, led by Suleiman the Magnificent personally. The Hungarian nobles, who still did not realize the dimensions of the approaching danger, did not heed their King's call to the colours. Louis II ordered them to encamp on 2 July but no one reported on that day – not even the King. Only when Louis himself furnished an example with his appearance in the camp did things start to move. The Hungarian war council – without waiting for their reinforcements only a few days march away – made a serious tactical error by choosing the battlefield near Mohacs, an open but uneven plain with some swampy marshes.
The Hungarian army was divided into three main units: the Transylvanian army under John Zápolya, charged with guarding the passes in the Transylvanian Alps, with between 8,000 and 13,000 men; the main army, led by Louis himself (beside numerous Spanish, German, Czech and Serbian mercenaries); and another smaller force, commanded by the Croatian count Christoph Frankopan, numbering around 5,000 men. Due to geography, the Ottoman army's ultimate goal could not be determined until it was crossing the Balkan Mountains. Unfortunately for the Hungarians, by the time the Ottoman army had crossed, the Transylvanian and Croatian army was further from Buda than the Ottomans were. Contemporary historical records, though sparse, indicate that Louis preferred a plan of retreat, in effect ceding the country to Ottoman advances, rather than directly engaging the Ottoman army in open battle.
The Hungarian forces chose the battlefield, an open but uneven plain with some swampy marshes near Mohács leading down to the Danube. The Ottomans had been allowed to advance almost unopposed. While Louis waited in Buda, they had besieged several towns and crossed the Sava and Drava Rivers. Louis assembled around 25,000 to 30,000 soldiers (with Croatian and Polish contingents and about 800-1,000 soldiers of the Papal States) while the Ottoman army numbered around 50,000. However, military history books from the 21st century calculate the number of the Ottoman Army around 100,000 men. The Ottomans are said to have numbered over twice as many — though this figure is exaggerated — and had up to 160 cannon. "The Hungarian army was arrayed to take advantage of the terrain and hoped to engage the Ottoman army piecemeal. The only advantage the Magyars had that day was that their troops were well-rested, while the Turks had just completed a strenuous march in scorching summer heat. But rather than attacking their fatigued enemy then, the Hungarians just watched as they struggled through the marshy terrain. It would have been "unchivalrous" to attack the enemy when they were not yet ready for battle.
Hungary built up an expensive but obsolete army, structured similarly to that of King Francis I at the Battle of Pavia mostly reliant on old fashioned heavily armoured knights on armoured horses (gendarme knights ). The Hungarian line consisted of two lines, the first with a center of mercenary infantry and artillery and the majority of the cavalry on either flank. The second line was a mix of levy infantry and cavalry.
Like the uncertainty over the number of actual combatants, there is debate over the length of the battle. Its starting time is generally placed between 1:00 PM and 2:00 PM, but the endpoint is difficult to ascertain. While some historians have placed the length of the battle at two to three hours, this seems unlikely given several important factors. The Ottoman army did not retreat from the field and enter camp after the battle; instead, they remained on the field all night without food, water, or shelter. Given that the Ottoman historians all note that it was raining, it seems likely that had the battle been short and ended early in the afternoon, by 5:00 PM at the latest, the Sultan would have ordered his army to camp or at least to return to their baggage. The few reliable sources indicate that Louis left the field at twilight and made his escape under cover of darkness; since the sun would not have set until 6:27 PM on 29 August 1526, this would imply that the battle lasted significantly longer than two to three hours (perhaps as long as four or five).
As the first of Suleiman's troops, the Rumelian army, advanced onto the battlefield, they were attacked and routed by Hungarian troops led by Pál Tomori. This attack by the Hungarian right was successful in causing considerable chaos among the irregular Ottoman troops, but even as the Hungarian attack pressed forward, the Ottomans rallied with the arrival of Ottoman regulars deployed from the reserves. While the Hungarian right advanced far enough at one time to place Suleiman in danger from Hungarian bullets that struck his cuirass, the superiority of the Ottoman regulars and the timely charge of the Janissaries, the elite troops of the Ottomans, probably overwhelmed the attackers, particularly on the Hungarian left. The Hungarians took serious casualties from the skillfully handled Turkish artillery and musket volleys. The Hungarians could not hold their positions, and those who did not flee were surrounded and killed or captured. The result was a disaster, with the Hungarians advancing into withering fire and flank attacks, and falling into the same trap that John Hunyadi had so often used successfully against the Ottomans. The king left the battlefield sometime around twilight but was thrown from his horse in a river at Csele and died, weighed down by his heavy armor. Some 1,000 other Hungarian nobles and leaders were also killed. It is generally accepted that more than 14,000 Hungarian soldiers were killed in the initial battle.
Suleiman could not believe that this small, "suicidal" army was all that once powerful country could muster against him, so he waited at Mohacs for a few days before moving cautiously against Buda.