Reddit mentions of The Nile tributaries of Abyssinia, and the sword hunters of the Hamran arabs

Uhh, Ethiopia's borders largely predate European colonialism. Unless by "colonial powers" you also mean Egyptians and Turks, in which case I agree to some extent, but still largely the modern borders of Ethiopia were drawn by Ethiopians themselves, such as when the Abyssinians conquered Harar and annexed and colonized the emirate ( https://en.wikipedia.org/wiki/Battle_of_Chelenqo ). Abyssinia was, famously, never colonized, btw, even though it was briefly conquered a couple times, such as by Ahmed Gragn and by the Italians, but neither conquest lasted long enough to be of note in the long run.

For instance, regarding the Abyssinia-Sudan border, here's a book you can read (1861) https://www.amazon.com/tributaries-Abyssinia-sword-hunters-Hamran-ebook/dp/B004UJ0YT4 . Even then, well before the European scramble for Africa, the Atbara river was the border between the countries, with a large and uninhabited "no mans land" in between the Atbara and the highlands that was depopulated due to the frontier warfare between Sudan and Abyssinia. Gallabat and Metema were already border towns in 1860, paying taxes to both the Abyssinian government and the Egyptian government.

The modern border with Eritrea is also based on pre-colonial borders, where much of modern Eritrea was an Ottoman colony for hundreds of years.

Ethiopia is pretty much the ONLY sub-Saharan African country where the European's scramble for Africa did not substantially affect its borders...