This occurred after the Ethio-Adal wars changing the demographic of Ethiopia forever.
Bali was the 1st province to be captured.
Within 50 years the Oromo were waging wars against organized states & conquering lands 500 miles away from their original homeland.
Their migration is well documented in the chronicles of Ethiopian Kings, Portuguese Jesuits, the Muslim state of Adal as well as eye witness accounts by the 16th C. Gamo monk Bahrey who wrote extensive works on their history.
There are entire indigenous groups who no longer exist like the people of Damot (present day Wollega) that were wiped out completely.
The Somali of the Hararghe highlands were assimilated & confederated into the Afran Qallo Oromo clan.
Despite the attacks core provinces remained in Ethiopian control & Emperor Sersa Dengel retaliated.
Many of our emperors, bravest warriors, and brightest stars are Oromo.
However this narrative of Ethiopia colonizing Oromos is a joke & we won't ignore history to appease nationalists
This paper by HS Lewis in the Journal of African history is a great place to start
cambridge.org/core/journals/…