Royal intermarriage is the practice of members of ruling dynasties marrying into other reigning families. It was more commonly done in the past as part of strategic diplomacy for national interest. Although sometimes enforced by legal requirement on persons of royal birth, more often it has been a matter of political policy or tradition in monarchies.
In Europe, the practice was most prevalent from the medieval era until the outbreak of World War I, but evidence of intermarriage between royal dynasties in other parts of the world can be found as far back as the Bronze Age.Cohen, p.165 Monarchs were often in pursuit of national and international aggrandisement on behalf of themselves and their dynasties,Thomson, pp.79–80 thus bonds of kinship tended to promote or restrain aggression.Bucholz, p.228 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. It could also enhance the prospect of territorial acquisition for a dynasty by procuring legal claim to a foreign throne, or portions of its realm (e.g., colonies), through inheritance from an heiress whenever a monarch failed to leave an undisputed male heir.
In parts of Europe, royalty continued to regularly marry into the families of their greatest vassals as late as the 16th century. More recently, they have tended to marry internationally. In other parts of the world royal intermarriage was less prevalent and the number of instances varied over time, depending on the culture and foreign policy of the era.
Africa
At times, marriage between members of the same dynasty has been common in Central Africa.Dobbs, David
Marriages between the Swazi, Zulu and Thembu royal houses of southern Africa are common.'Wedding Brings Xhosa, Zulu Tribes Together', LA Times For example, the daughter of South African president and Thembu royal Nelson Mandela, Zenani Mandela, married Prince Thumbumuzi Dlamini, a brother of Mswati III, King of Eswatini.Keller Elsewhere in the region, Princess Semane Khama of the Bamangwato tribe of Botswana married Kgosi Lebone Edward Molotlegi of the Bafokeng tribe of South Africa.'The Bafokeng: Getting royalty right ', News24.com, 13 November 2012
Other examples of historical, mythical and contemporary royal intermarriages throughout Africa include: Princess Mantfombi Dlamini, sister of Mswati III of Eswatini, and Goodwill Zwelithini, King of the Zulus, as his chief queen consort'Nelson Mandela: A Unique World Leader Dies At 95', Nigerian Echo The Toucouleur emperor Umar Tall and Princess Maryem, the daughter of Sultan Muhammed Bello of SokotoKobo, p.46
Pharaoh Amenhotep III alone is known to have married several foreign women: Gilukhepa, daughter of Shuttarna II of Mitanni, in the tenth year of his reign; Tadukhepa, daughter of his ally Tushratta of Mitanni, around Year 36 of his reign; a daughter of Kurigalzu I of Babylon; a daughter of Kadashman-Enlil I of Babylon; a daughter of Tarhundaradu of Arzawa; and a daughter of the ruler of Ammia (in modern Syria).
Asia Babylonia and Assyria There are a few recorded cases of intermarriage between Assyrian and Babylonian royals. According to legend, the Babylonian Semiramis was married to the Assyrian general Onnes and then to the Assyrian king Ninus, the legendary founder of Nineveh according to the Ancient Greeks.The Library of History by Diodorus Siculus, Vol. 1, The Loeb Classical Library, 1933. Retrieved on 2015-03-08 from http://penelope.uchicago.edu/Thayer/E/Roman/Texts/Diodorus_Siculus/2A*.html. She has been equated with the historical Shammuramat, wife of Shamshi-Adad V. In turn, Shammuramat has been claimed to be of Babylonian descent. In the early 9th century BC, the Babylonian king Nabu-shuma-ukin I (Dynasty of E) exchanged daughters in marriage with the contemporary Assyrian monarch. The Assyrian princess Muballitat-Sherua, daughter of Ashur-uballit I, was given in marriage to the contemporary Babylonian monarch. She was the mother of the future Babylonian king Kara-hardash. Additionally, Kurigalzu II was either the son or grandson of Muballitat. Other consorts of Assyrian monarchs, such as Naqiʾa, Ešarra-ḫammat, Banitu (who was perhaps brought to Assyria as a hostage after Tiglath-Pileser's conquest of Babylon) might also have been of Babylonian origin.
Babylon and Elam Babylonians and Elamites engaged many times in royal intermarriage, especially in the Kassite period. It is probable that Elamites and Kassites had close ties long before the first attested royal intermarriages between them. Babylonian Kassites and Elamites intensively intermarried for a period of about 120 years, from c. 1290 to 1170 BC. The royal intermarriages in this period were: Pahir-ishshan to eldest daughter (princess) of Kurigalzu II (1290); Untash-Napirisha to daughter of prince Burnaburiash (1250); Kidin-Hutran to daughter of prince [...]-duniash (1230); Shutruk-Nakhunte to the eldest daughter of Melishihu. Also Napirisha-Untash (c. 1210 BC) and Hutelutush-Inshushinak (c. 1190) are thought to have married Babylonian Kassite princesses. A man of Elamite origin, Mar-biti-apla-usur, the founder of the so-called Elamite dynasty, reigned in Babylon from around 980 to 975 BC, though the identity and origin of his consort are unknown. He might not have been himself from Elam but a Babylonian partially of Elamite origin.
Thailand The Chakri dynasty of Thailand has included marriages between royal relatives,Dobbs but marriages between dynasties and foreigners, including foreign royals, are rare. This is in part due to Section 11 of 1924 Palace Law of Succession which excludes members of the royal family from the line of succession if they marry a non-Thai national.Liu & Perry
The late king Bhumibol Adulyadej was a first cousin once removed of his wife, Sirikit, the two being, respectively, a grandson and a great-granddaughter of Chulalongkorn.Thailand Country Study Chulalongkorn married a number of his half-sisters, including Savang Vadhana and Sunandha Kumariratana; all shared the same father, Mongkut.Stengs, p.275
Vietnam The Lý dynasty which ruled Dai Viet (Vietnam) married its princesses off to regional rivals to establish alliances with them. One of these marriages was between a Lý empress regnant (Lý Chiêu Hoàng) and a member of fishermen-turned-warlords Trần clan (Trần Thái Tông) from Nam Định, which enabled the Trần to then topple the Lý and established their own Trần dynasty.
A Lý princess also married into the Hồ clan faction, which later usurped power and established the Hồ dynasty after having a Tran princess marry their leader, Hồ Quý Ly.
Cambodia The Cambodian King Chey Chettha II married the Vietnamese Nguyễn lord Princess Nguyễn Thị Ngọc Vạn, a daughter of Lord Nguyễn Phúc Nguyên, in 1618.Mai Thục, Vương miện lưu đày: truyện lịch sử, Nhà xuất bản Văn hóa – thông tin, 2004, p.580; Giáo sư Hoàng Xuân Việt, Nguyễn Minh Tiến hiệu đính, Tìm hiểu lịch sử chữ quốc ngữ, Ho Chi Minh City, Công ty Văn hóa Hương Trang, pp.31–33; Helen Jarvis, Cambodia, Clio Press, 1997, p.xxiii. In return, the king granted the Vietnamese the right to establish settlements in Mô Xoài (now Bà Rịa), in the region of Prey Nokor—which they colloquially referred to as Sài Gòn, and which later became Ho Chi Minh City.
India In the Chola dynasty in southern India, Madhurantaki the daughter of Emperor Rajendra II married Kulottunga I the son of Eastern Chalukya ruler Rajaraja Narendra. This was to improve the relationship between the two royal houses and to straighten Chola influence in Vengai.
China
The Xiongnu practiced marriage alliances with Han dynasty officers and officials who defected to their side. The elder sister of the chanyu (the Xiongnu ruler) was married to the Xiongnu general Zhao Xin, the Marquis of Xi who was serving the Han dynasty. The daughter of the chanyu was married to the Han Chinese general Li Ling after he surrendered and defected. , p. 31. The Yenisei Kyrgyz khagans claimed descent from Li Ling. Another Han general who defected to the Xiongnu was Li Guangli who also married a daughter of the chanyu.
The Xianbei Tuoba imperial family of Northern Wei started to arrange for Han elites to marry daughters of the imperial family in the 480s. Some exiled Han royalty fled from southern China and defected to the Xianbei. Several daughters of Emperor Xiaowen of Northern Wei were married to Han elites — the Liu Song royal Liu Hui (劉輝) married Princess Lanling (蘭陵公主);. Princess Huayang (華陽公主) to Sima Fei (司馬朏), a descendant of the Jin dynasty; Princess Jinan (濟南公主) to Lu Daoqian (盧道虔); Princess Nanyang (南陽長公主) to Xiao Baoyin (蕭寶夤) from Southern Qi. Emperor Xiaozhuang of Northern Wei's sister Princess Shouyang was wedded to the Liang dynasty ruler Emperor Wu of Liang's son Xiao Zong (蕭綜).
When the Eastern Jin dynasty ended, Northern Wei received the Jin prince Sima Chuzhi (司馬楚之) as a refugee. A Northern Wei princess married Sima Chuzhi, giving birth to Sima Jinlong. Northern Liang prince Juqu Mujian's daughter married Sima Jinlong.
The Rouran Khaganate arranged for one of their princesses, Khagan Yujiulü Anagui's daughter, Princess Ruru (蠕蠕公主), to be married to Gao Huan, the Han ruler of the Eastern Wei.Gao Huan, as demanded by Yujiulü Anagui as one of the peace terms between Eastern Wei and Rouran, married the Princess Ruru in 545, and had her take the place of Princess Lou as his wife, but never formally divorced Princess Lou. After Gao Huan's death, pursuant to Rouran customs, the Princess Ruru became married to Gao Huan's son Gao Cheng, who also, however, did not formally divorce his wife.
The Kingdom of Gaochang was made out of Han colonists and ruled by the Han Qu family that originated from Gansu. Jincheng Commandery (金城; Lanzhou), district of Yuzhong (榆中) was the home of the Qu Jia. The Qu family was linked by marriage alliances to the Turks, with a Turk being the grandmother of King Qu Boya.
Tang dynasty (618–907) emperors and the rulers of the Uyghur Khaganate exchanged princesses in marriage to consolidate the special trade and military relationship that developed after the khaganate supported the Chinese during the An Lushan Rebellion.Veit, p.57 The Uyghur Khaganate first exchanged princesses in marriage with Tang China in 756 to seal the alliance against An Lushan. The Uyghur Khagan Bayanchur Khan had his daughter Princess Pijia (毗伽公主) married to Li Chengcai (李承采), Prince of Dunhuang (敦煌王) and son of Li Shouli, Prince of Bin, while Princess Ningguo of the Tang dynasty married Uyghur Khagan Bayanchur. At least three Tang imperial princesses are known to have married khagans between 758 and 821. These unions temporarily stopped in 788, partly because stability within China meant that they were politically unnecessary. However, threats from Tibet in the west, and a renewed need for Uyghur support, precipitated the marriage of Princess Taihe to Bilge Khagan.
The ethnically Han Cao family ruling Guiyi Circuit established marriage alliances with the Uighurs of the Ganzhou Kingdom, with both the Cao rulers marrying Uighur princesses and with Cao princesses marrying Uighur rulers. The Ganzhou Uighur khagan's daughter was married to Cao Yijin in 916.
The Cao family also established marriage alliances with the Saka Kingdom of Khotan, with both the Cao rulers marrying Khotanese princesses and with Cao princesses marrying Khotanese rulers. A Khotanese princess who was the daughter of the king of Khotan married Cao Yanlu.
The Khitan Liao dynasty arranged for women from the Khitan Xiao consort clan to marry members of the Han (韓) clan, which originated in Jizhou (冀州) before being abducted by the Khitan and becoming part of the Han elite of the Liao.Biran 2012, p. 88.Cha 2005 , p. 51.