The Battle of Agincourt was a battle of the Hundred Years' War that resulted in an English victory. The battle took place on Saint Crispin's Day, October 25, 1415.
The English were commanded by their King, Henry V. The French were under the command of Charles d'Albret, the Constable of France.
Though outnumbered 5 to 1 by the French, the English inflicted as many as 10,000 casualties on the French, with the loss of just 600 of their own men. The French army was routed and destroyed.
The lesson is in choosing the ground on which to fight a battle. King Henry picked his ground carefully and made the French fight him on his chosen ground. The field of battle was condensed into a narrow ground "hemmed in by dense woodland." The French also had to walk through a great deal of mud to reach the English. In the end, the French couldn't exploit their superior resources to overwhelm the English.
In 1599, William Shakespeare immortalized the battle in one of his historical plays, Henry V. The clip below is from a 1989 movie of the same name, based on play: