Historical Information
Henry V is set during the Hundred Years war between England and France.
The Hundred Years war started out as a territorial dispute between France and England, it intensified as England found more and more success claiming french land, before being beaten back, loosing all their previous invasion had gained. This is where Henry V begins, a young king determined to see his nation back to its former glory.
The Battle of Agincourt
The decisive moment of Henry's Campaign came on a field outside the town of Agincourt. The English army was attempting to return to Calais where they could resupply. The English army was also attempting to escape from the much larger French force sent to face him. The only reason there was battle at all was that the French outmaneuvered Henry and their army was positioned between him and Calais. The battlefield was a muddy stretch of grass between two forests.
The Armored knight made up most of the power of the French army. While they would typically be mounted, Henry's knights fought on foot at Agincourt, as they were defending a position in the mud. The French knights on their horses charged straight at the English and were slowed considerably by the heavy mud.
The English longbow-man became famous because of what they did to the French in that muddy field. The knights and nobles of France were dragged through the mud and shot full of arrows. The French mercenary crossbowmen were also driven back by the longbows superior range, however the sheer number of French knights and the fact that the knights did not flee easily meant that Henry's dismounted knights eventually became involved in brutal hand to hand fighting. The longbow-men once again proved their worth by being able to flank the mass of now dismounted French knights, and their light armor meant they could run through the mud and find weak points in the French line. This was the final straw for the exhausted French knights, the ones who could run away did, and the rest surrendered to Henry. He had won against all odds.
Further information about the battle can be found here, https://www.youtube.com/watch?v=VDnKciXrmnc