The Battle of Agincourt took place on October 25, 1415, between French and English troops near the town of Agincourt in Northern France, during the Hundred Years War. The most interesting and important fact about this battle is that the French army, which had a significant numerical superiority, suffered a crushing defeat. The reason was the English use of archers armed with longbows. As a result of the defeat at Agincourt, the French were forced to sign a treaty in Troyes in 1420, according to which the English King Henry V was declared the heir to the French throne.
Preparing for Battle
Henry V invaded France in 1415, claiming the title of the French king. He besieged the port of Harfleur, which had strategic importance. The port was by no means easy prey. The English army, suffering heavy losses from disease, continued the campaign. Only on October 8, Henry sent most of his troops to Calais, where the English could wait out the coming winter and recover. The French collected a large force in Rouen. After the English king began a retreat to the north, the French began an active pursuit of the British army to block it off. Initially, the French were successful. The armies met on October 24, near the village of Agincourt, not far from Calais. The rain fell all day.
The British were exhausted by a marsh, a lack of provisions and illnesses. Henry understood that, and he was forced to engage in a battle in order to be able to continue withdrawing  to Calais. The French were better armed; in addition, they numerically outnumbered the English.
Composition of Troops
On the battlefield, the French were superior in number; but it is impossible to accurately determine the number of French soldiers who participated in the battle. Â Up to 60% of the French army consisted of heavily armed cavalry, consisting of knights and nobility. The rest of the army consisted of soldiers recruited from the garrisons of French cities and fortresses, and mercenaries from the cities of Northern Italy. The French had a large number of foot soldiers, consisting mainly of poorly trained commoners recruited among the peasants. The French infantry also included archers, but the French preferred to use a crossbow.
The English army consisted of a large number of professional soldiers. Most of the English infantrymen were armed with longbows, proven to be effective in battles. The rest of the infantry fought with spears, halberds, and swords. Some of the riflemen were mounted on horses, to give the troops greater mobility. There was a comparatively small number of heavy cavalry.
Battle
The French cavalry, with no order, attacked the English. The French knights were not disciplined. Secondly, the terrain did not allow them to bypass the British on the flank. Thirdly, the mud slowed the cavalry. French archers simply could not see the British, so they could not influence the course of the battle. English longbowman destroyed the French cavalry.
Under the hail of English arrows, the French knights, in heavy armor, were forced to cover a distance of 300 yards; Â very difficult in the mud. Having reached enemy positions, the French soldiers entered into hand-to-hand combat with the English. The French knights were physically exhausted and on foot. Armed with axes and swords, lightly armed English archers had an advantage over the tired, armored French knights.
Many French knights managed to escape, thanks to their servants. All the commanders of the French army were killed or captured in the battle. The English, despite their losses, won a complete victory. The English king, fearing a change in the course of the battle, and that a large number of poorly-guarded captive knights could draw weapons against the victorious Englishmen, ordered the prisoners to be killed. That was something unthinkable in those times.
Losses
The French suffered huge losses in the battle; three dukes, at least eight counts, one viscount, an archbishop, and dozens of dead representatives of the smaller French nobility. France lost a significant number of senior representatives of the military command. English losses were much smaller with one Englishman dead for every 10 Frenchmen. The number of dead French soldiers was estimated to be around 10,000.
Effects
Despite the fact that the English King won a great military victory, the political consequences of the battle were very complicated. The English King had to return to England, and a civil war started in France. The lack of unity in the country torn apart by war allowed the English King to prepare for a new campaign against France. Beginning in 1417, the new conquest was much easier for the English; taking into account the extensive damage caused to the French military and civilian structures in Normandy in 1415. After several years of military operations, the English King managed to achieve all of his planned goals. Under the terms of the Treaty of Troyes in 1420, he was recognized as regent and heir to the French throne. This was fixed by the marriage of Henry V with the daughter of the French King Charles VI, Catherine of Valois.
This battle demonstrated the superiority of the English longbow in its’ reach and strength. The arrowhead could not penetrate the armor of the French knight, only the slots and bare sections of the armor, as well as the horses, were injured. This led to the knights, having lost their horses, dismounting and getting bogged down with heavy boots and steel armor in the mud. Knights could not move in the muddy terrain because of their armor, and the light units of the English were quicker and more disciplined and organized. This battle marked the end of the era during which the most capable unit on the battlefield was a heavy knight. This set in motion a social change, from a feudal society to a society where most of the power was in the hands of an absolute ruler.
Sources:
Enguerrand de Monstrelet. Battle of Agincourt, 1415
Plan of the Battle for the Campaign of Azencourt (1415)