The southern part of what is now Myanmar was first settled by the Mons people who came into the area from the southwest coastal area. The Mons along with the related Khmer entered the southeast Asia region from the Mekong River valley area. The Burmans first settled in the north central Irrawaddy River valley area. They were preceded in that area by the Pyu's who were culturally related to the Burman tribes.
Yangon (Rangoon)
The city of Yangon (Rangoon) developed at the site of the Shwe Dagon pagoda. This pagoda had been a purely religious site long before the town of Dagon was declared there by the Mon king in the early 1400s. The Burman king Alaungpaya conquered the Mons kingdom on the Lower Irrawaddy in 1755 and renamed the town at the site Yangon, which means end of war strife in Burmese. Rangoon is just an inaccurate transliteration of Yangon.
King Alaungpaya wanted to develop Yangon as a port to replace the port of Syriam. There may have been concern about the security of Syriam which had been captured by Portuguese mercenaries in the early 1600s.
The demographic character of Yangon changed dramatically over the years. In the late 19th century it was more cosmopolitan than Burmese in character.