Are all dependent countries of China. Why can Vietnam be king and North Korea be king?

Because of its geographical location, North Korea is easily targeted by the Central Plains Dynasty. Vietnam is located in the south, out of the control of the central plains dynasty, so North Korea does not dare to proclaim itself emperor, while Vietnam does.

In feudal society, China was a superpower with many subordinate countries. The so-called subordinate countries are inferior to China in science and technology, China in culture and China in force. In order to get some help, they recognized China as their suzerain country, provided some local specialties every year, and sent troops to help during the war. Korea and Viet Nam were once vassals of China.

The Tang Dynasty claimed that all countries came to Korea, and Li Shimin, Emperor Taizong, was called Tiankhan, because there were many subordinate countries in the Tang Dynasty, and most of them wanted to get some technology from the Tang Dynasty and then go back to develop their own country. They will show respect for the Tang Dynasty and call themselves Xiao Wang when writing, but some countries are different, such as Vietnam.

Vietnam is a very strange country, which can be said to be ungrateful. In order to get benefits, you can be cheeky. Once you get the benefits, you will turn your back on others. His geographical position has miasma as a barrier and he is not afraid of the attack of the Central Plains regime. However, once you see a warm smile, you kowtow like a grandson and turn your head to dominate the country. Being an emperor is actually just Vietnam's complacency, and the Central Plains regime is unwilling to take care of him because it is too far away.

Why is North Korea not like Vietnam? Because North Korea is very close to the Central Plains regime, once there is any change in North Korea, the Central Plains regime will soon be able to send troops, so North Korea dare not be too arrogant. At least in the era of the prosperity of the Central Plains regime, North Korea has always stayed away from the Central Plains regime.