Why does Vietnamese language seem to be so similar to Mandarin Chinese

Question

I experienced many times how relatively easy it is to learn Chinese (its writing system excluded) for Vietnamese, comparing to Koreans or Japanese whose countries belong to the same zone of Chinese influence.

1. Why is that so? As far as I know, Chinese and Vietnamese do not belong to the same language family.
2. Was Chinese presence much more imposing in Vietnam than it was in Korea and Japan?
3. If certain features like: tonality of both languages, influence this phenomenon, then why these languages from two different families are both tonal in the first place?

Answer 1

It is easy for Vietnamese to learn Mandarin because they are already familiar with Chinese grammar and structure

• Vietnam was under Chinese influence for most of its history
• There were many waves of Chinese migration to Vietnam. Because of this, Vietnamese also has another category of Chinese loan words that Korean and Japanese lack, which are called từ Hán Việt Khẩu Ngữ. Khẩu Ngữ are words derived straight from Chinese dialects through oral transmission, as opposed to the literary language. Majority of these came from Cantonese and Teochew, eg: tả pín lù, tài xế, hầm bà lằng, ca la thầu etc. And in regions with heavy Chinese settlement, words for family members such as "a hia" for brother, chế for sister
• Chinese literature is quite popular in Vietnam giving Vietnamese a lot of exposure to chinese sentence structure and grammar
• A lot of Chinese idioms are still used in Vietnamese so Vietnamese are familiar with Chinese word order and word usage. Eg môn đăng hộ đối, danh chính ngôn thuận, danh bất hư truyền,

Answer 2

By way of analogy, English speakers find it relatively easy to learn romance languages, or Germanic ones. Much Middle English vocabulary was introduced by the Norman conquest, and much Old English vocabulary was derived from Germanic influences via the Saxons and Jutes. Approximately 60% of Vietnamese vocabulary derives from common sources shared with Cantonese - particularly from the Bai Yue ethnolinguistic complex. Simultaneously, Mandarin derived from the confluence of Cantonese antecedent dialects and the Manchurian language. Common sources seem adequate to explain the bulk of the affinity.

In general, phylogenetic purity is a characteristic of didactic simplifications, rather than of adequate explanations. As in biology, so too in diachronic linguistics: The generative axioms of signification may derive, for example, from the major language group, while vocabulary is dominated by sources in geographic neighbors of another group entirely. While I am not expert in Vietnamese historical etymology, it is my impression that Vietnamese may be an exemplar of this paradigm.

Certainly it is true that the borders of the southern Chinese and the Vietnamese dynastic empires have fluctuated significantly over the centuries of the historical epoch. In this regard, a closer Euro-centric analogy might be the Ukranian-Russian pair.