In the year 1444 AD, the Kingdom of Scotland had very little to pride itself over, other than the fact that it still existed north of England, despite England's best efforts. Its monarch was the somewhat unremarkable King James II of the House of Stuart, reigning since 1437 from the tender age of 6. At the very young age of 14, James II ruled a nation considered a backwater in Europe.
That changed on the 11th of November, 1444.
That night, the young King claimed to have received a vision from God, stating that his destiny was to save his people from oblivion, that Scotland was the last hope of the Celtic peoples. He also claimed that if he would work to restore the Celtic people, then he would hold God's favor in all his endeavours.
To that end, in 1445, King James II declared war on Antrim as a means to gain a foothold in Ireland, thus beginning the Irish Wars. The wars would rage for 15 years, with the Scottish continuing their actions against the Irish Clans and Lordships. Where the English had failed for centuries, the Scottish had managed to successfully execute within 15 years. Truly, it seemed that God was on the side of the Scots.
By 1453, most of Ireland had been subdued, but one obstacle remained: the Pale of Dublin, the last area of actual English control on the island. Scotland, however, knew that the Irish Clans were one thing, but England was another problem entirely. To try and find a solution to the eventual problem, Scotland approached France to turn its guarantee of independence into a proper alliance, reforming the Auld Alliance between Scotland and France. The motion was successful, as France also had eyes on the English holdings in Normandy and Gascogne.
In 1460, the Scottish armies had finally subdued all of Ireland outside the Pale, and had moved its armies to the English Border. Scotland, however, waited for France to make the first move. It came in 1462, when the French invaded Normandy and Gascogne. The English began moving as many of their troops to the mainland, and in 1463, the Scots pounced, honoring their alliance and invading Northumberland and the Pale.
The First Scottish Conquest lasted for 5 years. During which, the bulk of English forces were engaged by the French, allowing the Scots to invade as far south as Wales, capturing Cardiff. Dublin fell in 1466, and the Isle of Man was captured by an assault in 1467. The English had been beaten into submission, and surrendered most of Northumberland, northern Wales, the Pale of Dublin, and the Isle of Man to the Scots. In the French part of the war, England lost all its mainland territories barring the Pale of Calais to France.
With England beaten into submission, the Scots took the opportunity to begin integrating the newly conquered territories into its realm. Each new territory was created as a separate "Realm" within Scotland. Ireland was a separate entity within Scotland from Scotland proper, just as Northumberland was, Northern Wales, and the Isle of Man. These territories were given a larger degree of autonomy within Scotland in order to pacify the newly conquered lands.
Scotland had risen from being a European backwater to a rising power. England was on the retreat, and James II had become loved by the denizens of the Scottish homeland as the greatest King of Scots that had ever lived. Sadly, however, James II died in 1469. His son, James III, ascended to the throne. And with him, a new, grander idea came into position, one that sought to secure the "glory of the Celts" once and for all.