Short answers, pulled from the story.
Theravada Buddhism first reached Laos in the 7th century through the kingdom of Dvaravati. This early transmission occurred alongside tantric Buddhist influences arriving from Nan-chao, an ethnically Tai kingdom located in modern-day Yunnan, China.
Fa Ngum established the Lao state in 1353 CE with his coronation at Luang Prabang. He brought a Khmer Theravada teacher named Phramaha Pasaman to serve as head priest who introduced the revered Buddha image known as the Phra Bang.
Official Marxist theory rejected religion as a tool used by ruling classes to mislead oppressed people yet the Pathet Lao reconciled aspects of Buddhism with Marxism. Attacks against Buddhism mounted at the beginning of 1976 when teaching religion and Buddhist morality was prohibited in primary schools before pressures ceased by the end of that year.
By 1979, 1000 monks were reported confined to re-education camps according to refugee reports. The eighty-seven-year-old Sangharaja of Laos Venerable Thammayano fled to Thailand floating across the Mekong on a raft made from inflated car inner tubes in March 1979.
Official attitudes toward Buddhism began liberalizing in tandem with economic reforms in the late 1980s. By the early 1990s Buddhism was on the resurgence again with lines of monks accepting morning offerings from the faithful without interference.