For a three-act plot analysis, put on your screenwriter’s hat. Moviemakers know the formula well: at the end of Act One, the main character is drawn in completely to a conflict. During Act Two, she is farthest away from her goals. At the end of Act Three, the story is resolved.
Henry decides to invade France.
Henry's troops face a likely defeat at Agincourt.
Against all odds, Henry's army is victorious at Agincourt. Henry forces the King of France to name his as his heir and marry him to his daughter.