Since the Western Zhou Dynasty, China's marriage system has implemented the principle of "the same surname and no marriage", the Tang Dynasty with the same surname is a marriage sentence of two years, the Ming and Qing laws stipulate that those with the same surname are married, each cane sixty, but in the law does not prohibit marriage between cousins.
In order to consolidate the power of the Lü family, Lü Hou also married his granddaughter to Liu Ying, the Emperor of Hanhui, while the Habsburg family in Europe also adopted close relatives to consolidate power, and the family continued from the beginning of the 11th century to the end of the First World War. It is the most extensive feudal family in European history.
The Habsburgs, originating from Rudolf I, who in 1273 were elected Holy Roman Emperor, defeated Ethuka, annexed his territory, bought the remaining royal succession to Babenburg, persuaded Bavaria to cede the land north of Enns, and occupied Keinten.
But the Habsburgs wanted to occupy every piece of land in Europe, and they chose to marry outwards, and in order to ensure the purity of their blood, they married close relatives, Carlos II was the last king of the Spanish Habsburg dynasty and the only heir to the Spanish throne.
Since Spain and Holy Rome belonged to the same Habsburg family, under the influence of close marriage, Carlos II was the king of the Habsburg family with the most genetic diseases, he was frail and sickly from an early age, suffering from intellectual disability and epilepsy, the jaw bulge was also the most serious, because the jaw was too large, he could not even chew, in terms of appearance, he could not even be called a human.
When Carlos II was born, all four of his brothers died and succeeded to the throne at the age of 4, because of the problem of heirs, Carlos II married Marie Louise, lord of Orléans, the niece of King Louis XIV of France, in 1679, but after marriage, Carlos II was diagnosed with infertility and he could not have children.
On 1 November 1700, Carlos II died at the age of 38, ending the Habsburg dynasty in Spain, but the War of the Spanish Succession broke out due to the Holy Roman Empire's claim to the Spanish throne and the dissatisfaction of Britain and the Netherlands with Spanish relations in France.
This war was the last European war launched during the reign of Louis XIV, the "Sun King" of France, and France and Spain also went into decline, and Britain rose under the rule of Queen Anne. As for the Holy Roman Empire, in 1806 it gave up the title of Roman Emperor and ruled only in Austria.
Franz Joseph I was the last glory of the Habsburgs, he married Princess Sissi, the 22nd marriage between the two families, son Rudolf committed suicide for treason, and with the assassination of Crown Prince Franz Ferdinand in Sarajevo, which directly triggered the First World War and the final collapse of the Austro-Hungarian Empire.
In Europe, descent was extremely important, and in order to inherit the throne, one had to have a bloodline, which made the marriage of close relatives more frequent, and the marriage of Philip IV of Spain and Mariana of Austria was a marriage between an uncle and a niece, and Carlos II was not only their son, but also the cousin of his father's nephew and mother.
After generations of transmission, these genetic diseases have been infinitely magnified, and the bloodline is becoming more and more "pure", the most famous of which are the "shoehorn face" and "thick lips", although this is for the Habsburg throne, but it is also this intermarriage that eventually led to the collapse of the dynasty.