Historical Background for Shakespeare's HENRY V
The Hundred Years War was the result of a quarrel over which family had the right to the throne of France. Charles IV was the last of the Capetian line in France, and when he died in 1328, the crown passed to a new family, the House of Valois. But that family was challenged by King Edward III of England (1327-77) of the Plantagenet dynasty, who claimed the French crown through his mother, Isabella, sister of Charles IV. King Edward led a series of invasions of France, marked by notable victories at Crecy (1346) and at Poitiers (1356), but by the end of the 14th century, the Valois kings had regained sovereignty over most of France.
During that period, there was contention over who was the rightful king of England as well. Edward III had been succeeded by his grandson, Richard II, who was deposed in 1399 by his cousin, Henry, Duke of Lancaster, who became Henry IV. Throughout his reign there was civil strife over whether Henry was the legitimate king. When he died in 1413, the throne passed to his oldest son, Henry V.
Shakespeare wrote a series of eight plays covering the period 1399-1485 in English history. Arranged chronologically by topic, HENRY V comes fourth in the series, following three plays about the deposition of Richard II and the troubles of Henry IV. Throughout the Henry IV plays, the king is troubled by the behavior of young Prince Hal, his heir apparent. But when his father dies and Hal is crowned King Henry V, he reforms himself and sets out to prove himself an admirable monarch. One of his first acts is to reinstitute the Plantagenet claim to the French throne.
The tone of the opening of the play reflects the young King's determination to demonstrate both to the French and to his own nobles that regardless of whether his father had the right to seize the throne from Richard II, he will show by his victory in France that his cause is just and that his claim has both human and divine support.
It helps that a bill was then being considered in Parliament which would redefine a great deal of Church property as falling under the jurisdiction of the crown and subject to taxation. The Bishops of Canterbury and Ely whose conversation opens the play need to have the King on their side; hence they strongly support his claim to France. It is also worth noting that the three men (Cambridge, Scroop, and Grey) who are exposed as traitors by the young King were motivated not only by French bribes but also by their support of another claimant to the English throne. (Eventually this other claim would result in the War of the Roses, in which the son of Henry V would lose his crown to the rival family, the House of York.)
The characters who lament the death of their old friend John Falstaff (Bardolph, Pistol, and Nym) were all acquainted with the King when he was the fun-loving Prince Hal (in the earlier plays), but once he became King, Hal had turned away from his former friends, especially Falstaff, to concentrate on serious matters of court.
All this would be known to the Shakespeare's audience, either through their knowledge of English history, their having seen the earlier history plays on the London stage, or both.