It was easier for Henry to pursue this arbitrary course because the
introduction of artillery had changed the art of war. Throughout the
Middle Ages the call of a great baron had, as Macaulay says, been
sufficient to raise a formidable revolt. Countrymen and followers
took down their tough yew long bows from the chimney corner, knights
buckled on their steel armor, mounted their horses, and in a few days
an army threatened the holder of the throne, who had no troops save
those furnished by loyal subjects.
But since then, men had "digged villainous saltpeter out of the bowels
of the harmless earth" to manufacture powder, and others had invented
cannon (S239), "those devilish iron engines," as the poet Spenser
called them, "ordained to kill." Without artillery, the old feudal
army, with its bows, swords, and battle-axes, could do little against
a king like Henry, who had it. For this reason the whole kingdom lay
at his mercy; and though the nobles and the rich might groan, they saw
that it was useless to fight.