Praised be Jesus and Mary, now and forever.
St. John of Capistrano was an outstanding Franciscan preacher who has been called the Apostle of Europe because he worked in so many different countries. He was a fighter who fought against sin, against heresy, and against the Turkish invasion. He was born in Capistrano, a town in the mountainous Abruzzo region of Italy, 25 miles from the city of L'Aquila. It was 1386, and the town was then in the county of Celano. I viewed that his father, Anthony, had received land from Louis I of Anjou. His father had come to Italy in the train of Louis and died prematurely, shortly after 1400, when our saint was a teenager. We don't know exactly how he died, but he may have been murdered.
For later preaching in Germany, St. John said more than once that in Capistrano he had had five main enemies, who in two days had slaughtered 12 of his relatives and burned his father's and mother's houses. After his father's death, he exhorted his mother not to remarry. Then, when he was about 18, he went to the University of Perugia to study law. The course of studies lasted six years, and he did very well. In 1413, he was appointed to serve as the judge for one of the quarters of the city, and he did so with great integrity and fairness.
Two years later, the city was occupied by rebels who opposed the government of Perugia, and St. John was locked in a tower. He tried to escape through a window, but fell and broke his leg. He was put then in the deepest, darkest dungeon to make sure that he wouldn't attempt another escape. One night, St. Francis of Assisi appeared to him and invited him to become a friar. Interestingly, St. Francis's own conversion had also begun in a prison at Perugia. St. John bought his freedom with a hefty ransom and then told his wife what God had called him to do. This was an arranged marriage between nobles, but they hadn't lived together yet. He got a dispensation to enter the Franciscan Order and gave her back her dowry. Then he gave the rest of his goods to the poor and did public penance for the sins of his youth.
He was clothed at the Seraphic Convent on October 4th, 1416, and professed vows exactly a year later. Then he went to the friary of Fiesole, outside Florence, to study for the priesthood. There he had St. Bernardine of Siena for his guardian and professor and St. James of the Marches as a fellow student. These saints, together with Blessed Albert of Sartiano, are known as the four pillars of the Franciscan Observance. This was a Franciscan reform that, in the 1400s, embraced a stricter observance of the rule in a prudent manner. 
St. John of Capistrano distinguished himself among the Franciscans for great virtue and for the knowledge that God had infused into his heart. For this reason, the Franciscan Minister General, William of Casale, named him commissioner for all the Cis-Alpine Observance. That is, he was the one who governed, in the name of the Minister General, all the Franciscans of the Observant Reform on the Italian side of the Alps. At this time, all the Franciscans were still united under a single General Superior, despite the fact that they were divided into different reforms.
St. John showed such good sense in this role that he was then sent to reform the friaries of the Balkans and the Holy Land, and then those in Lombardy, France, and Spain. When his teacher, St. Bernardine of Siena, was accused of heresy for the way he was spreading devotion to the Holy Name of Jesus, St. John defended him in a debate before the Pope. As long as the saint lived, his main task was to preach in a wide variety of places against the various errors of his time. 
He fought the heresies of the Fraticelli and the Hussites. The Fraticelli, or spirituals, were a Franciscan reform gone wrong that reduced all of religious observance to the practice of poverty. The Hussites anticipated some of the teachings that would later be embraced by the Protestants.
His apostolate was confirmed by miracles. For example, to restore peace between the inhabitants of Rieti and Cantalice, he instantaneously healed a man whose head had been split open in a brawl between them. In another town, he commanded a possessed woman to spit out the devil that she had in her body, and a black slug came out and took the form of a burned stick. On another occasion, he brought back from the dead a pregnant woman who had been killed by an angry bull.
In 1451, he preached in Brescia for three days. Eyewitnesses say that over 2,000 sick people were brought to him, and he healed over 200 of them, holding in his hand the cap that St. Bernardine had used and signing them with the cross. 
What was he like? The man who later became Pope Pius III wrote, "I saw him in Vienna, small in stature, just skin and bones, but always cheerful in mood and strong in spirit, tireless in work, very learned and eloquent. His sermons were daily attended by 20 or 30,000 men who, although they did not understand the language he spoke, nevertheless listened more attentively to him than to the interpreter."
In the last years of his life, the threat to Christendom from the East grew. In 1453, the Turks conquered Constantinople. In the following two years, the Sultan Mehmed II campaigned in Serbia and conquered it. The popes tried to organize a crusade to stop the Turks, but the Christians were too divided politically. By 1456, the Turks were marching on Belgrade, which then guarded the border of Hungary. Meanwhile, the Pope had asked St. John of Capistrano to preach the crusade against the Turks, to use his powerful eloquence to gather the Christians to resist this invasion.
When the saint learned that Belgrade was in danger, he went there as quickly as possible, bringing the small force that he could gather and arriving there on July 2nd. There he received a revelation that they would ultimately be victorious. When the huge Turkish army arrived with its cannons and ships, St. John departed with a few religious to get more troops, promising he'd return. The Turks blockaded the Danube with 200 ships to keep supplies or troops from reaching the city and began bombarding it with their artillery.
In person, by letters, and by sending out preachers, St. John gathered a large force of crusaders to relieve the besieged city, but most were common folk, poorly equipped and without military training. John Hunyadi also came to the defense of Belgrade. He was then governing Hungary until the heir to the throne came of age. His force was smaller, but it was made up of professional soldiers, most of whom were mounted on horseback. But before they could reach the city, they had to eliminate the blockade. So first, Hunyadi gathered two fleets of boats to attack the blockading ships. One traveled down the Danube and the other upstream, so that they attacked the Turkish ships from both sides on July 14th. 
St. John had told the troops to invoke no other name than Jesus on water or land. They destroyed the blockading fleet, so troops and supplies could now enter the city. Every day, more crusaders arrived, mostly small groups led by a priest carrying a banner of St. Francis, St. Anthony, St. Louis IX, or St. Bernardine. They sounded more like a pilgrimage than an army. Few nobles had answered the call to the crusade. They were mostly farmers, poor people, students, religious, hermits, and tertiaries. They had no horses, lances, or breastplates, but came like David against Goliath with slings and sticks. Besides these, there was John Hunyadi's army and the original defending force, but they were a third or less of the Christian force.
The sultan was angry that the siege had been broken and troops were continuing to arrive. He had his artillery continue to pound the fortifications for a week and then launched a large-scale assault on July 21st. By now, the wall had been breached, towers had been knocked down, and the citadel was badly damaged. It was very questionable whether they could resist, but by invoking the name of Jesus, the defenders managed to repel the attack. The following day, the crusaders went out to attack the Turks in their camp. The Turks gave battle, but an eyewitness says that they panicked after the crusaders began invoking the name of Jesus. Captured Turks said that they had been terrified by strange voices they heard in the air. The sultan personally entered the battle and was wounded. Given this and their losses on the battlefield, they retreated.
However, after the victory, the plague spread throughout the land, taking the lives of both leaders, John Hunyadi and St. John of Capistrano. The latter died on October 23rd, 1456. He was beatified in 1650 and canonized in 1690. In 1984, St. John Paul II named him the patron of all military chaplains.
Praised be Jesus and Mary, now and forever.