On this day in 1469, 20-year-old Ferdinand of Aragon married 18-year old Isabella of Castile.  On the surface, it sounds like another wedding between a couple of young royals.  In reality, it turned out to be one of the most consequential marriages in world history.

First, it united all of the dominions of Spain into what would become the world's foremost military power.

Years later, they sponsored Columbus's trip, and the rest is the good history we used to learn in school before the P.C. crowd decided to spoil our celebrations of Columbus Day.  The trips convinced the royal couple to encourage colonial activity in the New World, leading to a period of great prosperity and imperial supremacy for Spain. 

In 1492 — or, incredibly, the same year that Columbus departed on his trip, they ordered all Spanish Jews to convert to Christianity or face expulsion from Spain.  The Muslims were also driven out of Spain during their very consequential reign.

They were what we would call today a power couple, as Kathy Copeland Padden wrote:

They had an incredibly modern relationship in many ways, with Isabella on an equal par with her husband.  They enjoyed a profound love and mutual respect in their relationship, tirelessly working together to achieve their aims.

In Ferdinand and Isabella's estimation, their crowning achievement wasn't expanding their empire to include the New World, or uniting the various dominions that would become modern Spain.  They believed their greatest accomplishment was driving out all Muslims from their country.

Ferdinand died in 1516 and Isabella in 1504.

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Image: Wenjie, Zhang | A Certain Slant of Light via Flickr, CC BY 2.0.