I enjoyed reading your post. Thanks for educating me.As early as thousands of years ago, Ancient Korea had surrendered to China. They have been affiliated to China for a long time.
For thousands of years, China did not choose to annex Ancient Korea, but to protect Ancient Korea, of course, there is a reason.
China's protection of North Korea is based on history, which is our cultural tradition and responsibility. China will not annex North Korea for the same reason.
Korean civilization is a branch of Chinese civilization, but it is a strong branch. The Korean people have a strong national consciousness, let them to join China will only bring instability within China.