This is recorded in a book written by a russian military officer, who accompanied Menelik during his campaigns in South Ethiopia. Amara Bantu say this was done to subjugate the Oromos/Gallas.
Menelik subjugated The Galla Regions and left many african oromo bantu families in disaster.
It seems Menelik was more cruel than the White colonists who did not amputate women breasts.
