This theme is not unique to Westeros; similarities to it can be found throughout history. Take, as just one example, the betrothal in A.D. 442 of Eudocia - daughter of Valentinian III, Emperor of Rome - to Huneric - son of Gaiseric, King of the Vandals. Since, at the time, Eudocia was only three years old, the wedding was delayed for several years.
Valentinian III died on March 16, 455 at the hands of two Hunnish assassins before the marriage took place (it was Valentinian III who sent Pope Saint
The Emperor Maximus broke the agreed upon betrothal by marrying Eudocia to his own son, Palladius, to strengthen his ties with another noble Roman family (one of whom would later declare Christianity the official religion of the Roman Empire and ban pagan religions altogether (it was not, contrary to what is written in many high school textbooks, Constantine who did this). Naturally, this did not please King Gaiseric who responded by marching his armies to Rome to sack the city.
They arrived on this day in the year 455. Pope Saint
The Emperor Maximus fled and was murdered by a Roman mob; his son Palladius may also have been murdered. Eudocia was taken captive and eventually married to Huneric as originally planned.
The sack of the Imperial City by the Vandals marked the fourth time in less than half a century that an army of barbarians approached the gates of the city. It was clear that the end of the Western Empire was near.