Moses King of Ethiopia

Shalom and thank you for your question. You would like to know the source for the idea that Moses ruled over the land of Kush (what is known as Ethiopa today apparently). I will translate for you the quote from the Midrash Yalkut Shimoni on chapter two of the Torah portion of Shemot, remez 168.

“In those days there was a war between Kush (translated as Ethiopia) and Bnei Kedem, and it came to pass when there was a siege on Kush. Moses fled Egypt and came to the camp of Kokanus the king of Kush. And Moses was eighteen years old at the time he fled, and the duration of the siege of Kokanus was nine years, and the young man (Moses) would come and go with them and the king and the ministers and the soldiers liked the young man because he was great and cherished and his stature was like that of a cedar and his face was like the shining sun and his strength was like that of a lion, and he became advisor to the king. And behold at the end of nine years the king became ill with the illness from which he would die and it came to pass that on the seventh day from his falling ill that he died, and his servants embalmed him and buried him.

“And they said one unto another what shall we do? And now we should crown a king over us and sit in the siege until the city falls into our hands. They hastened and removed their garments and threw them on the ground and made a large stage and put Moses to sit on it and they blew horns and said ‘Long live the King, Long live the King’ and all the ministers and all the people swore to give him the lady, the wife of Kokanus as a wife, and they coronated him over them.

“And Moses was twenty-seven years old when he ruled over the people of Kush, and he became strengthened in his rulership and he fought (their wars) and the days that he ruled over Kush were forty years. And he was successful in all his wars because G-d the L-rd of his fathers was with him. In the fortieth year of his kingship while he sat on his throne and the Queen was seated to his right and the lady said to the ministers and to the people ‘Behold it has been forty years that he has ruled and has not approached me (intimately) and has not worshipped the god of Kush. Now hearken please unto me, sons of Kush, that this one shall not rule over you, behold my son Muncham will rule over you for it is better to serve the son of your lord than to serve a strange person, a slave to the king of Egypt… ‘ And they gave him big gifts and sent him off in honour and he left there and he ceased to be king over Kush.”

Note that Moses ruled over Kush for forty years, not only ten.

We hope this information has been helpful and welcome further questions.