At Agincourt in 1408, the longbow was a decisive factor. At Flodden 105 years later, the longbow did not play an important role. What changed to end the longbow's importance in Medieval English warfare?

Although movies such as Braveheart and shows like Outlander like to portray the various wars between England and Scotland as an underdog story or a clash between complete opposites, with the rugged, masculine, freedom of the "noble savage" highlanders contrasted to the decadent, oppressive, and effete English, the two armies that faced off at Flodden Field were not really all that different. Likewise, the grand nationalist mythology that surrounds the Hundred Years War in English popular memory holds little resemblance to the actual Battle of Agincourt.

It is true that longbows were an important component of the English victory at Agincourt, but not because of anything intrinsic to the weapon itself. The English at Agincourt made a number of good tactical decisions. They picked their ground very well, so that they only had to fight on a narrow front that helped prevent any outflanking. They successfully maneuvered to put themselves in bowshot range of the French before the French could order their lines for a proper attack. The English also set up field fortifications in the form of stakes set into the ground that helped shield their vulnerable archers from cavalry assault. Even with these advantages, Agincourt came down to a lengthy period of desperate hand-to-hand combat that might have readily gone the other way for the English. Was archery important to their victory? Yes, but not so much because the longbow was such an effective weapon on its own. I went into the debate over the longbow's "killing power" here. The short version is: the longbow isn't actually all that effective at penetrating plate harness (at anything over point-blank ranges, that is). Knights wearing plate armor of the kind that was developed by the time of Agincourt aren't going to be dying in huge numbers from archery. Some are going to die, others might be wounded, but all of them are going to be hearing the arrows come down and hit the ground or their friends all around them. It forced the French to attack in a highly disadvantageous way, at a time when the French army was extremely disordered to begin with, and at a moment when they were unable to deploy effective missile support of their own to answer the English with. This is not to argue that the English archers weren't useful in winning the battle, but they were less decisive than the common myths of Agincourt would lead you to believe.

At Flodden Field, the Scottish army was a royal force led by James IV in person. It was not a motley collection of Highland noble savage stereotypes that media like Braveheart, Rob Roy, or Outlander like to portray. James IV had a force of armored pikemen supported by gunpowder artilley and advised by experienced French officers. Less armored Highlanders were involved in the battle, but they were by no means the majority of the Scottish force. James IV's attempted tactics at Flodden were initially somewhat similar to the English at Agincourt. He intended to force the English into attacking him in a strong defensive position, where he could bring his guns and archers to bear on their advance. However, the English managed to bring their guns up first, forcing James to order an attack lest his troops get picked apart by cannonfire. The Scottish advance suffered under the English guns, but were relatively unharmed by the English archers due to their armor. By 1513, the armor industry in Europe had developed even beyond what it had been in 1415 for reasons that /u/waritter is more qualified to describe than I am. Making armor had become much cheaper, allowing states and rulers to purchase larger quantities of breastplates, helmets, and other defenses for their new armies, which were increasingly becoming more professional forces consisting of pikemen, arquebusiers, gunpowder artillery, and cavalry. The Scottish army at Flodden was no impoverished rabble, but a fairly modern force in terms of equipment and tactics. Higher-quality, less expensive armor helped hasten the end of an era where archery had much battlefield utility and accelerated the need for troops equipped with handheld firearms, but this was a slow transition over the course of the 16th century in England. Even after Flodden Field, the longbow continued to be used in England, where military forces were increasingly not up to par with the troops fielded by the great continental powers.