Excerpts from Books and Wikipedia
Henry V faced almost certain defeat as his army was outnumbered with about 6,000 men vs. 20,000-30,000 French. "The key to the unlikely outcome at Agincourt was terrain. . . . A densely packed mass of French knights floundered forward in heavy armor across soft, muddy ground, harassed by a rain of arrows. . . . Henry's death in 1422, aged thirty-four, undid all these arrangements, denying the battle any long-term consequences." [Furtado: 1001 Days] "Agincourt was the third of a trio of great English victories--after Crecy and Poitiers--won by English archers over heavily armoured French men-at-arms. . . . However, the total dominance of the English archer was drawing to an end by 1415, with the emergence of gunpowder and the increasing use of firearms." [Battles of the Medieval World] "The turning point in the Hundred Years' War for 15th-century England that leads to the signing of the Treaty of Troyes five years later, making Henry V heir to the throne of France." [Wikipedia: Timeline of Middle Ages]