Editing Plaek Phibunsongkhram (section)

== As a Prime Minister of Thailand ==
On 16 December 1938, Phibun replaced Phraya Phahonphayuhasena as the Prime Minister of Thailand and as the Commander of the Royal Siamese Army. Phibun became the ''de facto'' dictator of Thailand and established a military dictatorship, consolidating his position by rewarding several members of his own army clique with influential positions in his government.

Later he proceeded the nationalism policies to the point of [[ultranationalism]], and to support this policy he launched a series of major reforms known as the Thai Cultural Revolution to increase the pace of modernisation in Thailand. His goal "Aimed to uplift the national spirit and moral code of the nation and instilling progressive tendencies and a newness into Thai life".

His goal of cultural modernisation are banning the people to chew the gums, abolishing to wearing the loincloth for women, supporting to wearing hats, banning Thai musicals but supports international musicals.

On 24 June 1939, Phibun changed the country's official English name from "Siam" to "Thailand" at Luang Wichitwathakan's urging. The name "Siam" was an exonym of unknown and probably foreign origin, which conflicted with Phibun's nationalist policies.

In 1941, in the midst of World War II, Phibun decreed 1 January as the official start of the new year instead of the traditional ''Songkran'' date on 13 April.

=== Songsuradet Rebellion ===
Colonel Phraya Songsuradet, who was Phibun's rival, previously conflict with Phibun before 1932 Revolution, by Phraya Songsuradet's planner of revolution, Later Phibun asked him for his alternative plan for cope if revolution failure, but Phraya Songsuradet did not answer him, but asked back to Phibun and he didn't have plan too, later they are argued in midst of conference, After the conference, Phibun thinks that Phraya Songsuradet shouldn't live together with him in the world, as Phibun wants to kill him very bad, which developed conflict til Songsuradet Rebellion in 1939.

=== Franco-Thai War ===
Phibun exploited the Fall of France in June 1940 and the Japanese invasion of French Indochina in September 1940, He believed that he have a chance to decisive eliminate the French imperialism, and Phibun believed Thailand could recover territories ceded to France by King Rama V because the French would avoid armed confrontation or offer serious resistance. Thailand fought against Vichy France over the disputed areas from October 1940 to May 1941. The technologically and numerically superior Thai force invaded French Indochina and attacked military targets in major cities. Despite Thai successes, the French tactical victory at the Battle of Ko Chang prompted intervention from the Japanese, who mediated an armistice where the French were forced to cede the disputed territories to Thailand.

=== Alliance with Japan ===
After Franco-Thai War, Phibun declared that Thailand becomes neutral or non-aligned country until Japan invaded Thailand for invading Burma, Later Phibun was reluctantly forced to order a general ceasefire after just one day of resistance and allow the Japanese armies to use the country as a base for their invasions of the British colonies of Burma and Malaya. On 21 December Phibun signed a military alliance with Japan. The following month, on 25 January 1942, Phibun declared war on Allied forces, Phibun purged all who opposed the Japanese alliance from his government. Pridi Banomyong was appointed acting regent for the absent King Ananda Mahidol, while Direk Chainam, the prominent foreign minister who had advocated continued resistance against the Japanese, was later sent to Tokyo as an ambassador. The United States considered Thailand to be a puppet state of Japan and refused to declare war on it. When the Allies were victorious, the United States blocked British efforts to impose a punitive peace.

=== Removal ===
In 1944, as the Japanese suffered many defeats and the underground anti-Japanese Free Thai Movement steadily grew in strength, the National Assembly ousted Phibun as prime minister and his six-year reign as the military commander-in-chief came to an end. Phibun's resignation was partly forced by two grandiose plans: one was to relocate the capital from Bangkok to a remote site in the jungle near Phetchabun in north central Thailand, and another was to build a "Buddhist city" in Saraburi. Announced at a time of severe economic difficulty, these ideas turned many government officers against him. After his resignation, Phibun went to stay at the army headquarters in Lopburi.