Emperor of the Valley

The protagonist's father had a dream and thought he was the destined emperor. Then a Taoist priest from a Taoist temple also made some calculations and said that he was the ninth emperor. So this small landowner who had never even been to the city proclaimed himself the emperor and founded the country in a small valley. (According to feedback from book friends, the pace of this book is super fast. He becomes emperor in just three chapters, and fights that overwhelm the country at every turn...)