1. Introduction

In the mid-nineteenth century the Chakri dynasty of Siam/Thailand produced royal offspring on a scale that is difficult to imagine today. King Mongkut (Rama IV, r. 1851–1868) fathered around 82 children with 35–36 wives and his son Chulalongkorn (Rama V, r. 1868–1910) had 77 children with 92 consorts, including four queens.

By contrast, the late King Bhumibol Adulyadej (Rama IX, r. 1946–2016) had four children with one queen, and the present king Vajiralongkorn (Rama X) has at least seven children in total, with only a handful counted as senior royals in the current order of succession.

This white paper examines why a dynasty that once generated hundreds of royal children per reign now appears demographically “thin,” and what legal, demographic, political, and cultural shifts produced this contraction.

2. Mid-19th-Century Baseline: A High-Fertility, Polygynous Court

2.1 Structural polygyny and reproductive strategy

Until the early 20th century, Siamese royal and elite marriage took place in a legal and social framework that openly recognized polygyny. Pre-1935 family law categorized wives into an official wife (mia klang muang), minor wives (mia klang nok), and slave wives (mia klang thasi), with children of all categories recognized as legitimate.

For kings this meant:

Dozens of consorts drawn from noble families. High numbers of births for dynastic security and for staffing an expanding bureaucracy with princes and princesses. Children as political capital: marriages and titles bound provincial nobility and urban elites to the throne.

2.2 Quantitative picture

Approximate numbers of children for mid-Chakri kings illustrate the regime:

Rama II – 83 children (34 sons, 39 daughters) by a queen, secondary wives and 55 concubines. Rama III – 51 children. Rama IV (Mongkut) – 82 children (39 sons, 43 daughters) from 35–36 wives. Rama V (Chulalongkorn) – 77 children (roughly one-third sons, two-thirds daughters) from 92 consorts.

Chulalongkorn’s sons and grandsons formed an exceptionally broad princely stratum. Yet even here we can already glimpse future “shrinkage”: of his 33 or so sons, only 15 produced male heirs, and many daughters never married because royal women were not allowed to marry commoners at the time.

3. The Legal and Institutional End of Royal Polygyny

3.1 The 1924 Palace Law of Succession

King Vajiravudh (Rama VI) promulgated the Palace Law of Succession (1924), which:

Clarified succession according to a type of male-line primogeniture. Ranked lines based on the status of mothers (queens vs lower-rank consorts).

This did not directly limit fertility, but it narrowed the number of lines considered dynastically important, turning many of Rama V’s descendants into sidelined collateral branches.

3.2 Abolition of legal polygamy (1935)

A more direct demographic break came with the 1935 revision of the Civil and Commercial Code, which made monogamy the only legally recognized form of marriage. The earlier categories of official, minor, and slave wives were abolished; any second marriage contracted while a first remained valid became void.

Polygyny could still be practiced informally or via “consorts,” but these unions had no legal marital status and weaker recognition for offspring. Since the late Chulalongkorn era, and definitively from Rama VI onward, kings themselves moved toward monogamy—Rama VI, Rama VII, Rama VIII, Rama IX all maintained a single queen and did not publicly maintain harems.

3.3 The 1932 Revolution and budgetary constraint

The 1932 revolution replaced absolute monarchy with constitutional monarchy. Over time this:

Reduced royal political power and constrained the size of royal households via budgets controlled by elected governments. Made a huge corps of princes and princesses politically sensitive: many were retired from official roles or relocated overseas. Encouraged a more compact “working royal family” model, closer to European constitutional monarchies.

4. Thailand’s Demographic Transition and Elite Fertility Decline

4.1 National fertility decline

Thailand as a whole experienced a classic demographic transition:

In the 1960s, total fertility rate (TFR) exceeded 6 children per woman. A highly successful National Family Planning Program from the late 1960s–1970s drove TFR below replacement (<2) within about two decades.

This shift reflected urbanization, education, and new ideals of small, educated families.

4.2 Elite and royal adoption of low fertility norms

Urban, educated elites – including the royal family – were among the first to adopt:

Later marriage and postponed childbearing. Smaller desired family size, as the costs of high-quality education, international study, and security for royal children rose. A strong emphasis on health and survival of a few children, rather than “numbers insurance” against high infant mortality.

Thus, while Mongkut or Chulalongkorn might view 40–80 children as rational insurance and patronage strategy, post-1960s royals behaved more like Western upper-middle-class families: two to four children as a norm.

5. Changing Rules About Who “Counts” as Chakri

The perception that the dynasty has “shrunk” is not only about births; it also reflects reclassification of who is considered part of the royal house.

5.1 Title dilution and generational downgrading

Thai royal titles step down in rank each generation through the male line:

Children of a king: Chao Fa / Phra Ong Chao (princes/princesses). Grandchildren in the male line: Phra Ong Chao or Mom Chao. Further generations: Mom Rajawongse and Mom Luang, increasingly close to commoner status.

By the late 20th century, studies of Rama V’s descendants estimate around 150 individuals with the rank of Mom Chao still alive, many great-grandchildren or great-great-grandchildren of Chulalongkorn, but no longer seen as core royals.

Thus, the total biological descent of the Chakri line remains large, but the “royal family” in public life has been narrowed to:

The reigning monarch and consort. Their children (and sometimes siblings). A small surrounding circle of high-ranking princes and princesses who perform official duties.

5.2 Restrictions on royal marriages and reproduction

In earlier generations:

Princesses could not easily marry commoners, which paradoxically reduced dynastic fertility: many Chakri princesses remained unmarried and childless.

In later generations:

Relaxation of these norms allowed more marriages to commoners, but descendants might lose royal status, especially when living abroad. Some princes/princesses chose career or education paths (diplomacy, academia, international organizations) that made large families impractical.

These legal and social filters continually winnow the visible royal core, even when descendants exist.

6. Individual Reigns After Chulalongkorn: Demographic Constriction in Practice

6.1 Rama VI (Vajiravudh, r. 1910–1925)

Married late, had no surviving legitimate male heir. His childlessness was one prompting factor for the 1924 Palace Law of Succession. This already represented a dramatic contrast with his father’s 77 children.

6.2 Rama VII (Prajadhipok, r. 1925–1935)

Married once, no children. Abdicated in 1935 and lived in exile in the UK; his childlessness symbolized the declining role of the monarchy in a constitutional order.

6.3 Rama VIII (Ananda Mahidol, r. 1935–1946)

Came to the throne as a child and died at 20, unmarried and childless.

6.4 Rama IX (Bhumibol Adulyadej, r. 1946–2016)

One queen (Sirikit), four children. Carefully cultivated an image of a modest, nuclear royal family to enhance moral legitimacy in a changing political environment.

6.5 Rama X (Vajiralongkorn, r. 2016– )

Has fathered at least seven children with several partners, but: Only some are fully recognized in the line of succession. No grandchildren yet, raising concern that the Mahidol branch (the current royal line descending from Rama V via Prince Mahidol) may fail in the 21st century.

The progression from tens of children per king (Rama II–V) to zero, zero, four, then seven with limited recognized heirs dramatically illustrates dynastic contraction.

7. Political Economy and Image Management

7.1 Fiscal prudence and public scrutiny

In a modern constitutional state:

A very large royal family is fiscally expensive (stipends, security, housing) and politically contentious. The monarchy’s legitimacy increasingly depends on being seen as disciplined, not extravagant.

Thus the number of royals supported by the Crown Property Bureau and the state budget is kept smaller than the biological pool of descendants.

7.2 Media, morality, and royal branding

From the mid-20th century:

Kings, especially Bhumibol, used the image of a stable, monogamous family to project moral authority. This implicitly disavowed the old court polygyny that had generated huge numbers of children. Excessive royal fertility could now undermine, rather than reinforce, the desired image of a modern, disciplined monarchy.

8. Structural and Cultural Summation: Why the Dynasty “Shrank”

Putting the strands together, the reduction from “hundreds of children” in mid-Chakri reigns to a small number of royal offspring today reflects several interacting factors:

End of legal polygyny and shift to monogamy 1935 family law abolishing polygamy, combined with earlier moves toward a single queen, sharply reduced the number of consorts and therefore potential births. Demographic transition and new fertility norms Thailand’s national fertility fall – driven by education, urbanization, and a highly effective family planning program – changed the ideal from “many” to “few but well-educated” children, especially among elites. Succession law and title downgrading The 1924 Palace Law and title conventions narrowed which lines and which generations count as “royal” in a constitutional monarchy, even as biological descendants proliferated. Political change and budgetary constraints The end of absolute monarchy and increased public scrutiny made it impossible and undesirable to maintain a vast, publicly funded network of princes and princesses. Marriage restrictions and changing gender roles Earlier rules that prevented high-ranking princesses from marrying commoners reduced their childbearing. Later relaxations allowed more marriages but often at the cost of royal status for descendants, shifting them out of the dynastic spotlight. Symbolic repositioning of the monarchy Kings from Rama VI onward deliberately styled the crown on European constitutional models, privileging a nuclear family image over a sprawling harem, which reduced reproductive scale and changed public expectations.

9. Conclusion

The “shrinkage” of the Chakri dynasty from monarchs with 70–80 children to today’s small number of recognized heirs is not simply a story of fewer births. It is a composite outcome of:

Legal reforms (end of polygyny, clarified succession). Demographic modernization (national fertility decline). Institutional downsizing and fiscal constraint. Changing gender, marriage, and career patterns among royals. Deliberate image management in an era of mass media and constitutional politics.

Biologically, the Chakri bloodline remains widely diffused through Thai society and diaspora networks. Politically and institutionally, however, the monarchy has consciously redefined itself as a compact, managed royal household, aligning reproductive behavior with the expectations and constraints of a modern nation-state.