At first King James IV had been reluctant to renew the alliance with France despite the urging of King Louis, wanting to remain neutral. However, his relations with England were beginning to become strained over the years. The fact that his sons Arthur and James [1] were third and fourth respectively in line for England's throne did not help matters nor did Parliament passing an act which called for him to be obedient to the King of England [2].
Even then the Scottish monarch offered no tangible help to France, only to renew the alliance. Unfortunately, neither the Dowager Princess nor the Duke of York saw it that way. The Archbishop of York [3] convinced Pope Julius to issue a ecclesiastical censure for the Scottish people. After Julius' death, King James tried to convince his successor, Pope Leo to countermand the interdict. Pope Leo did not and threatened King James with excommunication if he were to break the peace treaty.
King James was said to have muttered, "Which one?" before he declared war on England. Despite pleas from his heavily pregnant wife, the monarch had decided that he had no other alternative. He did send England notice a month in advance as he felt chivalry demanded it.
Upon receiving the warning, the Dowager Princess Katherine immediately ordered her son to be sent to Wales, put under the care of her late husband's childhood friend, Gruffydd. King Arthur now a boy of eleven refused to go, reminding his mother that John of Gaunt had been in battle at age ten. Katherine argued that John of Gaunt had only accompanied his older brother on a navel battle, he had done no fighting of his own. Arthur countered neither would she. He followed this by stating that he wanted his soldiers to know he was with them, not hiding in his castle like a coward. Katherine told him that was a lovely thought but he had years to defend his people. Right now they needed to see him safe and well. King Arthur reluctantly agreed.
Once her son was on his way to Wales, Katherine began to mobilize the army and buy the supplies needed while ordering Sir Thomas Lovell and the Duke of Norfolk to rise an army in the midlands. She had two banners made that displayed the royal arms of England and Spain.
Elizabeth of York temporarily came out of retirement to act as regent as Kathrine rode out, in full armor, to face the invading Scots. She would meet up with the Duke of Norfolk in Northumberland. She addressed the troops, telling them that while she was born in Spain, she had come to see England as her homeland and she would expel the invaders from her new home just as her parents had done for Granada. She reminded them of the last pretender who had dared mount an invasion and how he was swiftly dealt with. She finished by starting up a war cry: "For King Arthur!"
The battle of Flodden Field was a disaster for the Scots. First their artillery failed to work properly. Then when they were charging down Braxton Hill, they found the a marshy area at the foot of the hill. King James lost his balance [4], falling forward, nearly face first in the mud. He managed to get back up and rejoined his men. But by then, the English had already begun their slaughter. He was captured by Edmund Howard [5] and forced to surrender by the Duke of Norfolk who wryly commented that this time a duke did command a king, referencing an early barb King James had sent him when Norfolk had challenged him.
Katherine greeted the captured king when he was brought to her, noting she would be sure to send his bloodstained coat to her brother-in-law so he could use it as a banner as he ravaged the French's countryside. As his ancestor [6] had so many years ago, King James was sent to stay at the Tower of London. Edmund Howard was given the earldom of Hereford as a reward.
[1] Butterflies have flapped their wings and Prince Arthur, Duke of Rosthsay (b. 1508) lives longer.
[2] While I was doing my research of King James, I realized it was less him following the Auld Alliance and more him having a rivalry with King Henry.
[3] Christopher Bainbridge was the archbishop before Wolsey. He was King Henry's chaplain and a cardinal.
[4] Our first butterfly avoiding James' death.
[5] Kitty Howard's father, Thomas Howard the Elder's third son, and our second butterfly preventing King James' death.
[6] That would be King James I. He was imprisoned for eighteen years.