Myanmar
Mon, who form 2% of the population, are ethno-linguistically related to the Khmer. Overseas Indians are 2%. The remainder are Kachin, Chin, Rohingya, Anglo-Indians, Gurkha, Nepali and other ethnic minorities. Included in this group are the Anglo-Burmese. Once forming a large and influential community, the Anglo-Burmese left the country in steady streams from 1958 onwards, principally to Australia and the UK. It is estimated that 52,000 Anglo-Burmese remain in Myanmar. As of 2009[update], 110,000 Burmese refugees were living in refugee camps in Thailand.

Q: When did a mass migration of the community that  previously held a persuasive authority on the Burmese population start?
1958 onwards