I thought it was because the king of France expressed his comtempt for what he considered to be the young playboy king of England by sending Henry V a box of tennis balls. Young King Henry showed a bit of unbrage by invading France and beating the crap out of them at Agincourt.

The war went on for quite a while as I recall. A hundred years, wasn't it?

Oh, yes. And while it was going on, I think they burned a saint.,

Don Firth

P. S. Provided work for a number of people later on:   Bill Shakespeare, Lawrence Olivier, Kenneth Branaugh, Ingrid Bergman, many others. . . .