Marriage between royal family was often a way to secure / strengthen an alliance between two monarchs. For example, according to Wikipedia

Marriage between dynasties could serve to initiate, reinforce or guarantee peace between nations. Alternatively, kinship by marriage could secure an alliance between two dynasties which sought to reduce the sense of threat from or to initiate aggression against the realm of a third dynasty

I wonder, how this would work from the point of view of the dynasty that supplied the princess? For example, if you marry off your daughter, and she lives in the other monarch's family, of course it will somewhat restrain you from attacking them. But how does this guarantee (or at least increase the confidence) that the other monarch will not betray you? If anything it seemed the daughter can be used as hostage, a bargaining chip, or even mistreated by the other monarch in future conflicts.

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    Presumably your daughter, being a loyal sort of girl, would use her position in the other court to sway them away from any potential conflicts with your realm. Oct 4, 2015 at 18:12
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    Because then you'd be family. Your children would be together and your grandchildren would have both of your bloodlines. Legal kinship, for one reason or another, is considered a deeper bond in virtually all cultures and societies - political marriages are by no means limited to Medieval Europe. Of course, in practice, family is often sacrificed for political expediency.
    – Semaphore
    Oct 4, 2015 at 19:14
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    Kinship based alliances are not particularly rare, not limited to medieval Europe. Beside family ties, it also allows inheritance, so intermarrying two dynasties ties the wealth and crowns, too, not only just building on someones sentimental feeling about family.
    – Greg
    Oct 5, 2015 at 5:25

4 Answers 4


Such marriages were usually part of wider treaties, including a dowry, non-aggression and/or mutual support agreements. The king didn't just get a queen, he got a chunk of land, possible inheritance rights, not to mention preventing his enemies making the same pact with his wife's family. Foreign princesses were mistreated - Catherine of Aragon after Prince Arthur's death, and when Henry 8 divorced her, but I suspect the possible advantages of your daughter/sister being Queen of a foreign power outweighed, in terms of realpolitik, any potential abuse.

Amusingly, when Christiana of Denmark was offered the chance of marrying Henry 8, she replied that, had she two necks, the King of England would have been welcome to one of them!


If anything it seemed the daughter can be used as hostage or a bargaining chip

That could be an option if the sides were not on the equal terms. Say, if you have to show your loyalty to the conditions of some peace treaty after an unsuccessful war, then sending such "a hostage" may save you a couple of fortresses. After all, girls need husbands.

On the other hand, if you are on equal terms, then by this marriage you make another monarch to owe you. And this could be of much help, say, if you have both a daughter and a son.

But how does this guarantee (or at least increase the confidence) that the other monarch will not betray you?

Such marriages may also be the part of formal treaties between countries. And at the very least, just the fact of marriage effectively cancels out any previous casus belli.


If your daughter is the mother of the monarch's children, that would inhibit most monarchs from attacking you. After all, you're the children's grandparent (and monarch's parent in law). And the monarch hopes that his children will inherit from you, as well as him.

Not to mention the likely impact of "pillow talk." Unless the daughter hates you for some reason.


Several of the other answers have hit this, but I'm going to put the same idea in a slightly different way.

If I marry my daughter to the prince of FarOffIstan, then there is a chance that my grandchildren will rule the country. It is in my best interest to ensure that FarOffIstan is strong and prosperous. My daughter's husband's father shares that same interest.

For societies that conceive of wealth as land, marriage is quite literally an investment - deferred short term benefits will reap rewards for our descendants. (alternatively, think of it as a reverse tontine...) Both families will observe each other and measure how committed the other party is to the welfare of the Grandchildren. Both parties should fight & struggle to improve the future value of the investment.

Of course if either of the couple dies before the grandchildren are able to rule, there is the risk that the family of the surviving child will need to secure new investors (so to speak). If there is a grandchild, then a Regency council may preserve the value of the investment; if there is no grandchild, then all that effort has been wasted.

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