The Grand Duke of the New Empire

The protagonist transmigrates into the body of a foreign-world marquis’s son, inherits the marquis title, develops his fief, commands the surrounding nobles, and takes on both his own kingdom and neighboring countries, eventually becoming a grand duke. The protagonist has no System, no special abilities, and no harem. He relies solely on his knowledge of the twenty-first century and a thousand years of Chinese military wisdom to vie for supremacy over the realm.