Read the passage carefully and choose the correct answer.

Ethnic Groups

Vietnam is a multi-nationality country with 54 ethnic groups. The Viet (Kinh) people account for 87% of the country’s Population and mainly inhabit the Red River delta, the central coastal delta, the Mekong delta and major cities. The other 53 ethnic minority groups, totaling over 8 million people, are scattered over mountain areas (covering two-thirds of the country’s territory) spreading from the North to the South.

Among ethnic minorities, the most populated are Tay, Thai, Muong, Hoa, Khmer, Nung... with a population of around 1 million each, while the least populated are Brau, Roman, Odu with several hundred people each.

 

A number of ethnic minorities had mastered some farming techniques. They grew rice plants in swamped paddy fields and carried out irrigation. Others went hunting, fishing, collecting and lived a semi-nomadic life. Each group has its own culture, diverse and special. Beliefs and religions of the Vietnamese ethnic minority groups were also disparate from each other.

(http://ww.vietnamembassy.org.uk/population.html)

Why Vietnam is a multi-nationality country?