An interesting history lesson this week. We’re all used to stories about the inbreeding of monarchies across early modern Europe. Austria’s Hapsburgs led the way, marrying family members off left, right and centre as a diplomatic strategy. Then Queen Victoria took things to new levels – her descendants ruled not just the UK, but Germany and Russia, as the 20th century dawned.

It’s easy to scoff at the inbreeding involved, but hold off. Royal families hooking up with each other might not have been good for their gene pool, but it had a beneficial side effect: fewer wars. So argues a new study examining the monarchies of Europe between 1495 to 1918, mapping the dynastic links, and conflicts, between them.

The researchers show that when a kinship tie between monarchs ends, the chance of war increased significantly. For example, when two monarchs are linked via married children and that tie dissolves there is a 9.5 percentage point increase in the annual chance of conflict between their nations. The authors argue this is because “kinship ties between rulers lower negotiation costs and increase the peace dividend, increasing the likelihood of diplomatic resolutions to potential conflicts”.

Over those 400 years or so, the percentage of European monarchs that had family ties increased threefold. The authors argue this contributed to the dramatic decrease in the number of wars – and, in particular, the 50% drop post-1800. Nearly 45% of that decline can be attributed to greater ties between rulers, it’s suggested.

So next time the monarchists among you hear people scoffing at the cost of a royal wedding, you can remind them of something: peace is priceless.