Thailand (ประเทศไทย), officially the Republic of Thailand, was a regime in Thailand that lasted from 1941, when Field Marshal and Prime Minister Plaek Phibunsongkhram overthrew the country's king, and reformed the government. About a year later, the Japanese Empire occupied the country, and it later signed a mutual defense pact with Japan. Officially, the nation was a fascist republic, but it was realistically closer to being a military dictatorship. Japan allowed the country to function largely independently, and did not leave a garrison, giving Thailand much freedom. As a result, the Thais fared much better as part of the Greater East Asia Co-Prosperity Sphere than most other countries, which were mostly Japanese puppet states.
Under Phibunsongkhram, who ruled the longest of the three military dictators in the regime's history, the state was very nationalistic and pro-Japanese, supporting the idea of pan-Asianism. Thailand militarily aided Japan in the conquest of Burma, and continued providing support during the Burma Campaign. Thai troops also fought in the invasion of India. During the following Cold War, the Western powers attempted several times (unsuccessfully) to overthrow the military government in the Republic of Thailand. The regime outlived Japan itself, whose empire fell in 1993. Phibunsongkhram left his position in 1970 to another field marshal, and died later in 1998. His successor ruled for eleven years before being replaced.
The regime lasted until 1994, seeing the rule of three military dictators. The leading dictator was very old by that time, and thus a revolution was able to overthrow the government. Afterwards, the king was reinstated, and a new royal government was formed.