Right now I think the answer for this >>45664 is: economical factors. I have to look it up.

Also I'm really curious how a battle looks like there.

More also. If I understand correctly this conflict had two phases for now. In the first, the Tigrayans (who are not just Tigrayans but other folks, I think I'm gonna use the designation as the people who live in that region, regardless of ethnicity) were pummeled, and they conducted guerilla warfare, and the second when they gathered enough strength to step onto the battle field, forced out the govt. troops, and initiated their own offensive.
In short:
1. asymmetrical phase
2. conventional phase
These ofc can be divided further.

From the top of my head three conflicts with similar characteristics:
The campaigns against Scotland by Longshanks, the story of William Wallace, and Bruce and all that.
The Napoleonic War in Iberia, locals fighting as guerillas then Wellington arrived.
Vietnam has parallels with the Cong and the NVA both engaging with South and their allies.