https://www.cia.gov/library/readingroom/docs/CIA-RDP85T00287R000901070001-6.pdf
That’s an old CIA dossier from 1984 describing the back and forth that’s gone on between Addis Ababa and Khartoum just to give you an example of how close each plays the other. They played a hand in the other losing valuable territory. Really interesting to read seeing how things turned out.
Sudan has similar issues as Ethiopia. Lots of IDPs (each have a million), fragile transitional government passing reforms attempting to appease the young and dissatisfied masses, land disputes with neighboring countries. I’m not sure if South Kordofan has been resolved or if Darfur has been resolved. But I do know regarding this particular topic Ethiopia and Sudan have a highly militarized frontier at the Fashqa triangle where skirmishes took place just this past summer. So Sudan, though weak, is going to try to utilize the situation to their advantage.
Edit:
https://www.cia.gov/library/readingroom/docs/CIA-RDP85T00287R000500100001-7.pdf
Another memo discussing the TPLF when they were still a guerillas movement. Shows how close they were to the Eritreans and just how much they actually owed to them despite them acting as though they overthrew Mengistu alone. The Eritreans are a major reason why Ethiopia was freed from the Derg.