Margrave’s Bastard Son was The Emperor
62 Our main lead who is a king and a magician gets reincarnated/transported 500 years into the past. he becomes an illegitimate son and a magician. Everyone assumes he is illiterate but because he was reincarnated he is actually very smart and knows how to use magic. Since he is used as an leverage when making a pact with the savages he uses that in his advantage, and makes a deal with the savages to side with him. He eventually helps their vice-leader later get healthier and earns their trust and support. They help him take over his family and kill his father stepmother and step brother. He starts to side with the first prince, to help him with managing the estate and developing trade. He now also helps one of the border families. The border family's wife is abused by her husband, and he helps her take over the family after servant killed her husband.
I Became the Master of the Devil