Answer:
The Mekong Delta also known as the Western Region (Vietnamese: Miền Tây) or the ... Angkor Borei is a site in the Mekong Delta that existed between 400 BC-500 ... During the Middle Holocene the Mekong River was discharging waters into ... between 2005 and 2011, while 166,400 people migrated out in 2011 alone.
Explanation:
Sorry, I couldn't find anything about rivals, but I found this.
