Because of North Korea's geographical position, it is easy to be targeted by the Central Plains Dynasty. Vietnam is located in the south, and it is separated from the core controlled by the Central Plains Dynasty. Therefore, North Korea does not dare to claim the title of emperor, while Vietnam does.

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

The Tang Dynasty claimed that all countries came to Korea, and Taizong Li Shimin was known as Tiankhan, because there were many subordinate countries in the Tang Dynasty, and most of them wanted to acquire some technology in the Tang Dynasty and then go back to develop their own country. They would be respectful to the Tang Dynasty and call themselves Xiao Wang when writing, but some countries were different. Some countries were respectful on the surface, but they were arrogant at heart, such as Vietnam.

Vietnam is a very strange country. It can be said that it is ungrateful. In order to get benefits, it can be cheeky. Once it gets benefits, it will turn its face and deny people. Its geographical position is protected by miasma, and it is not afraid of the attack of the regime in the Central Plains. However, once the situation is not good, it will kowtow like a grandson and turn its head to dominate the country. Being the emperor is actually just Vietnam's self-satisfaction, and the Central Plains regime will not take care of him because it is too far away.

why isn't north Korea 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 when the Central Plains regime flourished, North Korea has always been respectful to the Central Plains regime.