In addition to The Crusades, all those big European military expeditions to the Middle East (and one time to Greece!) in the 11th-13th centuries, Christendom’s crusading fervor was also expressed in a number of smaller “crusades” that continued until the 15th century. Some of these smaller expeditions, like the “Alexandrian Crusade” of 1365, consisted of campaigns in the Middle East; others, like the Albigensian Crusade in the early 13th century and the Northern Crusades in the 12th and 13th centuries, targeted Christian “heretics” or the remaining pagan populations in Europe (these, in contrast to Crusades directed against Muslims, tended to go pretty well for the Crusaders). The Crusade of Nicopolis (which is often called the “Battle of Nicopolis” since it only took the one battle for the Crusade to completely collapse), in 1396, targeted Muslims, but Muslims on European soil. It went about as well as most other Crusades against Islam, in this case thanks to some top-notch stupidity from the French Crusader contingent.
During the period between 1185 and this Crusade, the Balkans, the Danube Basin, and the western Black Sea coastal region were controlled by the Second Bulgarian Empire. This was essentially a continuation of the First Bulgarian Empire (6th-11th centuries), after an interlude of about 170 years (1018-1185) when the Byzantine Empire controlled those areas.
Needless to say, the Bulgarians weren’t in such expansive shape by 1396, because a new player had arrived on the Balkan scene: the Ottomans. The 1389 Battle of Kosovo reduced the Serbians to the status of an Ottoman vassal and thereby secured Ottoman control over most of the Balkans. The Ottomans captured the fortress of Nicopolis (modern Nikopol, a town in Bulgaria) in 1393, which positioned them right in the heart of the Bulgarian Empire, and the remaining Bulgarian nobles then appealed to the King of Hungary, Sigismund (d. 1437), for relief. Hungary and the Venetian territories along the Adriatic coast were next in line to be run over by the expanding Ottomans, so Sigismund worked quickly to try to counter the Ottoman advance. This was still very early in Ottoman history, so I suspect the Europeans saw them more as an onrushing horde than as the stable, albeit very powerful, empire they eventually formed.
As a major Catholic monarch, Sigismund had the 14th century version of a direct line to the Vatican. Sure enough, Pope Boniface IX (d. 1404) declared a crusade the following year, in 1394. I should say that this was smack in the middle of that whole unfortunate Western Schism affair, so there was actually another pope running around at Avignon and Boniface’s authority wasn’t undisputed. But everybody seems to have understood how serious the Ottoman threat was, and soldiers from all over Europe — the Holy Roman Empire (which Sigismund would later rule, incidentally), France, Venice, Genoa, and more — heeded Boniface’s call and flocked to Sigismund’s banner. The Ottomans, meanwhile, were ruled by Sultan Bayezid I (d. 1403), who was known as Yıldırım, or “Lightning,” and not because he loved a good thunderstorm. Bayezid knew how to fight and he was quite successful in all of his campaigns (until the very last one, which was a total disaster, but we’ll get to that). He was joined by his Serbian vassals under Stefan Lazarević (d. 1427), the very capable warrior whom he’d set in charge of Serbia after the Battle of Kosovo.
There are wildly diverging accounts of the size of the two armies. Contemporary Christian sources, no doubt trying to explain the (spoiler alert) Ottoman victory, said that there were only about 16,000 Crusaders facing over 200,000 Ottoman soldiers. And, you know, why stop at 200,000? Why not a billion? Either size would have been equally plausible. Ottoman sources, probably trying to oversell the victory, said that about 60,000 Ottoman soldiers faced a Crusader army twice their size. Yeah, no. Modern historians estimate that the early Christian accounts probably got the size of the Crusader army about right, and that the Ottoman army was probably comparable, though the Ottomans may have outnumbered the Christians by as many as 10,000 soldiers. The Crusader army was the usual mix of upper class knights with lower class archers and infantry, but the Ottoman army was a little different than we’re used to seeing, in that the Janissary Corps wasn’t yet in existence and the Ottomans weren’t yet using firearms. These would have been mostly levies and raiders on horseback, probably a mix of heavy cavalry and light/horse archer cavalry, and they were joined by the Serbian heavy cavalry under Lazarević.
The Crusaders assembled at Buda (modern Budapest was created from the merger of the cities of Buda and, ah, Pest, on opposite sides of the Danube, in 1873, so for now it’s just Buda), where their chances of victory were immediately doomed by the same things that usually wound up dooming Crusaders: infighting among the commanders and an uncanny collective ability to choose the worst possible course of action at all times. Sigismund argued that the best course of action was to let the Ottomans come to them. But the French forces were the largest involved in the Crusade, and their de facto leader, Enguerrand VII de Coucy (d. 1397), insisted that the army should be bold and dashing, that it should take the offensive and march east, first to push the Ottomans out of the Danube and then to continue on to aid the now-constantly beleaguered Byzantines. Obviously we can’t know if Sigismund’s defensive strategy would have been more successful, but my point here is that it couldn’t really have been any less successful that Coucy’s plan, which was, par for the course, the one the war council adopted.
On September 12 the Crusaders arrived at Nicopolis and resolved to take the fortress. How they planned on doing this is anybody’s guess, because they didn’t actually have any siege machinery (which in hindsight is a point in favor of Sigismund’s defensive option), but they figured they had enough time to starve the garrison out. They were wrong, to put it mildly. After less than two weeks, long enough to let the Crusader army settle down and get bored but not long enough to starve out the defenders, word came that Bayezid’s army was approaching Nicopolis.
Sigismund, who had some familiarity with the way the Ottomans fought from talking with other Christian lords in the region, proposed that the army set up with its infantry in the front to deal with the Ottoman vanguard, which was usually composed of the worst Ottoman soldiers and was purely meant to hold the enemy’s attention while the much better mounted forces were free to move around, go for a flanking/enveloping maneuver, strike at the enemy’s weak spots, that kind of thing. But the French commanders butted in again, insisting that noble knights couldn’t possibly take second position behind a bunch of peasant infantry or whatever, and so they were stationed at the front of the Crusader lines.
When word came that Bayezid was nearby, Sigismund requested that the army stay put until his scouts could fully reconnoiter the Ottoman lines and report back, but again the French objected. This time it was a young French noble named Philip of Artois (d. 1397), who insisted that Sigismund was trying to deprive the brave French knights of their honor by delaying the advance, and though even Coucy thought that this was ridiculous, Philippe’s determination to march off immediately meant that the rest of the army could either follow him and stay together or let him go and watch part of the army get annihilated. They decided to stick together.
The French then led the rest of the army to its final set of blunders. Although accounts aren’t in total agreement on the details of the battle, they appear to have encountered the Ottoman vanguard as it was coming down a hill outside of Nicopolis, meaning that the mounted French knights were trying to charge uphill. As you might imagine, the charge was painfully slow, but even so the French knights were able to drive the irregular Turkish infantry off. Coucy now ordered his line to reform before proceeding, but the younger French nobles like Philip effectively told him to get bent, and continued charging up the hill piecemeal (though, to be honest, it wasn’t much of a cavalry charge at that point, since many of the horses had crapped out and a lot of the knights were on foot). Unfortunately for their chances at battlefield glory, they ran smack into the totally rested Ottoman cavalry, which routed the French line and captured many nobles, including the French army’s de jure commander, the very young John of Nevers (d. 1419). John was the highest-ranking noble in the French contingent but was supposed to defer to the far more experienced Coucy when it came to making decisions).
The Hungarians and other allied forces who were coming in behind the French must have felt like charging at the fleeing Frenchmen out of sheer anger, but they were too busy dealing with the Ottoman cavalry, which was not only charging down the hill but had availed itself of the confusion to flank and envelop the rest of the Crusader army. The final hammer came from the Serbian knights under Lazarević, whose cavalry charge turned the Crusader defeat into a rout. Sigismund was able to get to the Danube and escape on a boat to the Venetian ships that were stationed on the river, but whatever was left of his army surrendered. Many others tried to swim to those Venetian ships in full armor and drowned (I’m honestly not sure what they thought would happen when they dove into the river with ~80 or so pounds of armor on).
Although it signaled the end of the Second Bulgarian Empire (there wouldn’t be a third), the ultimate result of Nicopolis turned out to be temporarily indecisive, but that had nothing to do with the Crusaders. Bayezid got a fat ransom from King Charles VI of France for the return of all those captured nobles (Coucy and Philip of Artois were not among them; they died in captivity), plus firm control over the Balkans, but in 1402 he made the grave mistake of heading east to respond to the challenge of some wanna-be Mongolian conqueror named Timur. The whupping that Timur laid on the Ottomans at Ankara, and Bayezid’s subsequent death in captivity, sent the young Ottoman Empire into a decade-long interregnum/civil war, during which time much of the empire’s territorial gains in Europe were lost. Of course, once the empire stabilized again, the Europeans were unable to stop it from regaining what it had lost, and then some.