Short answers, pulled from the story.
Buddhism arrived in the 3rd century BCE when monks named Sona Thera and Uttara Thera traveled to a region called Suvannabhumi. Archaeological finds at Nakon Pathom reveal Dharma wheels, Buddha footprints, and Pali inscriptions dating back to the Mon kingdom of Dvaravati between the 6th and 11th centuries CE.
Prince Mongkut founded the Dhammayuttika Nikaya order after spending twenty-seven years as a monk before ascending the throne in 1851. This new sect kept stricter monastic discipline including restrictions on using money, storing food, or taking milk in the evening while emphasizing the original Pali Canon.
King Chulalongkorn made the new sangha hierarchy formal and permanent through the Sangha Law of 1902 which divided religious administration into four main divisions: north, south, center, and Dhammayutika Nikaya. Each division received one patriarch with a deputy under him and all elders formed the Sangha Council of Elders as the highest body of Thai Sangha.
Forest tradition monks like Ajahn Mun Bhuridatto (1870, 1949) and Ajahn Sao Kantasīlo (1861, 1941) developed ascetic practices seeking awakening through meditation during the early 20th century. Charismatic figures including Ajahn Maha Bua, Ajahn Chah, Ajahn Thate, and Ajahn Lee built influential communities as students of Ajahn Mun.
More than 20 Thai women have ordained since 2002 when the Senate reviewed the 1928 ban as unconstitutional though main Theravada orders Mahanikaya and Dhammayutika Nikaya yet officially accept fully ordained women into ranks.