Why did the north unify the south in history?

1. Physically, northerners are stronger than southerners, even horses. This is a great advantage of the cold weapon era, so it is easy to win in the war.

2. Many emperors like to build their capital in the north, so the development of the north is often more prosperous; However, hot flashes in the south are prone to disasters such as floods and plagues, so the development of the south is easily affected and destroyed.