Final answer:
Divine rulership and the preservation of sacred bloodlines have been historical practices in various cultures. Marriages among royalty were often incestuous, as in ancient Egypt, or influenced by social norms and laws, as seen in Silla. The divine right of kings doctrine additionally supported the idea of monarchs' absolute power derived from a divine source.
Step-by-step explanation:
The notion that rulers are considered divine and therefore must protect the purity of their bloodline by marrying within their own family is a historical practice observed in various cultures, notably in ancient Egypt and certain Hellenistic kingdoms. For instance, in Egypt, incestuous marriages among royalty were common as they were believed to maintain the divine essence of the royal family. This belief led to many health issues due to inbreeding. Similarly, in Hellenistic Egypt under the Ptolemaic dynasty, marriages between siblings like Ptolemy II and his sister Arsinoe were conducted to solidify power and proclaim divinity.
In different societies, such as Silla and the Inner Asian Steppe peoples, marriage customs were influenced by differing social norms and legislation, often forbidding intermarriage across ranks or involving practices like the levirate. Confucianism and other political and social idiosyncrasies also played a role in who could marry whom, with strictures against intermarriage affecting the social status and rank of offspring.
The divine right of kings was another concept that bolstered the idea of divine rulership, granting monarchs absolute power by virtue of their supposed divine selection. This doctrine was prevalent in various monarchies around the world. Notable in history, these intricate familial and social structures exemplify the complexity of marrying practices among ruling elites throughout different cultures and eras.