The Khana Ratsadon staged a coup d'état in Siam on 24 June 1932. It ended Siam's centuries-long absolute monarchy rule under the Chakri dynasty and resulted in a bloodless transition of Siam into a constitutional monarchy, the introduction of democracy and the first constitution, and the creation of the National Assembly. Dissatisfaction caused by economic crisis and incompetent government, as well as the rise of Western-educated non-royals to positions of influence, fueled the revolution.
King Prajadhipok remained on the throne and compromised with Khana Ratsadon. Two coups were mounted during the following year, in April and June, amid infighting within the government over Pridi Banomyong's socialist planned economy and a rebellion of royalists.
Since 1782, the Kingdom of Siam had been ruled by the Chakri dynasty. After 1868, King Chulalongkorn (Rama V) reformed a medieval kingdom into a centralising state of absolute monarchy. The monarchy started to make royal and nobility hierarchy, the Sakdina, to be the most critical aspect of Siam's political system. Towards 1880, Chulalongkorn asked of Europe an initiation into modern culture and showed a decided preference for England's Anglo-Saxon culture. In 1910s, King Vajiravudh (Rama VI) sought to legitimise absolutism through Thai nationalism, using a Western approach, by appointing more able commoners to the government. A commoner involvement disappointed the aristocracy and nobility. Rama VI carried out unpopular policies that lowered the influence of the royal family.
During the reign of King Rama VI, the government's fiscal health was eroded. Lavish spending on the court, inability to control the corruption of the King's inner circle, and his creation of the Wild Tiger Corps to promote modern-style nationalism were widely deemed as wasteful. By 1920, fiscal mismanagement and the global economic downturn took the state budget into deficit. In 1925, the most senior princes decided to demand large cuts in expenditures, especially the royal household. This represented a bold challenge to the authority of the absolute monarch and reflected the severity of the fiscal malaise in Siam. The critique was thus that Rama VI was not a competent absolute monarch, and that he squandered the massive political capital.
In 1912, a palace revolt, plotted by young military officers, tried unsuccessfully to overthrow and replace Rama VI. Their goal was to overthrow the ancien régime and replace it with a Westernised constitutional system and to replace Rama VI with a prince more sympathetic to their beliefs. The revolt failed and the participants were imprisoned. In reaction, Vajiravudh abandoned his attempts at constitutional reform and continued with his absolutist rule, with the minor exception of appointing some able commoners to his privy council and government.
Rise of the Western-educated "commoner" elites
Western education became popular in the reign of Rama V. Although this was still largely limited to the Siamese nobility and the wealthy, new avenues of social mobility were now available to commoners and members of the lower nobility. The best example of these commoner beneficiaries is Phibun Songkram who was from a peasant background. Many of the brightest Siamese students, both commoners and the nobility, were sent abroad to study in Europe. These include Pridi Banomyong, who was of Sino-Thai descent, and Prayoon Pamornmontri, the half-German son of a junior Thai official at the Siamese legation in Berlin and later a page to the crown prince who would become Rama VI. They were to become prominent members of the "promoters". These Western-educated commoner elites were exposed not just to the latest scientific and technical knowledge in Europe, but also to the ideals of Western democracy, nationalism, and communism.
In February 1927, in a hotel on the Rue du Sommerard in Paris, France, a small group of seven military and civilian students assembled to debate the founding of a party to try to bring change to Siam. Intent on not wanting to repeat the failure of the 1912 plot, they laid out a clear and coherent plan to change Siam. This group included two young students: one a soldier and an artilleryman Plaek Khittasangkha, the other a law student and radical Pridi Banomyong. The group called themselves the "Promoters" (ผู้ก่อการ), hoping to return home to try to promote change. The Promoters realised, ironically, as the king's advisors had done, that the Siamese people were not yet ready for democracy, and most were illiterate peasants with little concern for affairs in Bangkok. In Bangkok itself, the new and emerging middle class was dependent on the patronage of the aristocracy for jobs and positions. As a result, they realised that a "mass revolution" was not possible and only a military-led coup d'état was possible. For this purpose a vanguard party was formed and it was named the Khana Ratsadon (คณะราษฎร).
When the Promoters eventually returned to Siam by the end of the 1920s, they quietly expanded their lists of contacts and party membership, mostly using a personal relationship. Pridi became a teacher at the Ministry of Justice's Law School, where he gathered the support of about fifty like-minded men, mostly civilians and civil servants, who also wanted to see the end of absolute monarchy. It was the job of the others, such as Plaek, who had by then received the Luang title and became Luang Phibunsongkhram, to try to gather supporters within the army. A young naval captain, Luang Sinthusongkhramchai, was doing the same for the navy. The number of party members increased, and, by the end of 1931, it reached 102 members, separated into two branches consisting of civilians and the military.
Prayoon Pamornmontri, one of the seven Promoters, himself an army officer, and former Royal Page of King Vajiravudh, took it upon himself to try to recruit for the party influential and powerful members who also wanted to see the end of absolute monarchy and power of the princes. One officer he had a connection with was the Deputy Inspector of Artillery, Colonel Phraya Phahol Pholpayuhasena. An affable man and popular within the army, he immediately joined the party and gave it his support. The second senior officer was Colonel Phraya Songsuradet, considered one of the best minds of his generation and the Director of Education at the Military Academy. Both had studied abroad and were eager for change. Songsuradet instantly became the party's tactician, advising it should first secure Bangkok militarily and eventually the country would follow. He also advised the Promoters to be more secretive to avoid official and police detection. Eventually, he approached his friend Colonel Phraya Ritthiakhaney, commander of the Bangkok Artillery, who shared his concerns about the princes' domination over the army and eventually joined the party. Finally, they were joined by Phra Phrasasphithayayut, another discontented officer. Forming what was known within the party as the "Four Musketeers" (4 ทหารเสือ, Four Tiger Soldiers), the most senior members of the party they eventually became its leaders.
Modernized attempt of Rama VII
Prince Prajadhipok Sakdidej inherited a country in crisis. His brother King Vajiravudh had left the state on the verge of bankruptcy, and the fact that the state and the people were forced to subsidise the many princes and their lavish lifestyles. Prajadhipok created the Supreme Council of State to solve the problems. The council was composed of experienced senior princes, that quickly replaced the commoners appointed by Vajiravudh. The council was dominated by the Minister of the Interior, German-educated Prince Paribatra Sukhumbandhu, high-ranking Chakri princes had regained dominance of the government, and only four of the twelve ministries were administered by commoners or members of the lower nobility. Prajadhipok turned out to be a sympathetic monarch, immediately ordered a cut in palace expenditure and travelled extensively around the country. He made himself more accessible and visible to the ever-growing Bangkok elite and middle class by carrying out many civic duties. By this time, students sent to study abroad had started to return, faced with a lack of opportunity, the entrenchment of the princes, and the comparative backwardness of the country.