I can only give a rough idea. Royal marriages in Europe are messy, but they are generally related to politics. For example, there was a Saxon-Coburg-Gotha dynasty in Coburg, Bavaria, Germany. This country is very small, but because its Prince Abel married the famous Queen Victoria of England, almost all the royal families in Europe can shed this kind of blood, which shows the confusion of intermarriage. In short, there are many royal families in Europe, all of which are family units. Anyway, there are blood relations between the royal families in Europe now.

And this kind of intermarriage has different effects on the country. If the king of one kingdom dies, but there is no prince but only a princess, then the princess marries the prince of another kingdom and the two kingdoms merge, or the queen remarries to another king and the two countries merge. Of course, Queen Mary, like Louis XVI, wanted to establish a cooperative relationship with the French Bourbon dynasty because of the Habsburg dynasty in Austria. It has a great impact on all countries.

As for the European system, from the feudal dynasty autocracy, some became constitutional monarchy, and some experienced dual monarchy, becoming today's socialism or constitutional monarchy.