I think issue started with 2020 election. Baby Abiy postponed it citing COVID-19. Tigray went ahead and did the elections - and called Abiy illegitimate.
The central issues is Abiy attempt to centralize power - by forming prosperity party.
Previously each nation had their own parties.
Some were active in the regions - while others would form coalition nationally.
In any case that is water under the bridge. The war is on. The advantage has swing back to Abiy. Six months ago Abiy forces were fleeing Tigray. Now they are back with drones.
How will Tigray respond to this? They go and hide in their hills?
Right now they are asking their allies in Western to impose non flight zone and embargo on arm sales....but will China and Turkey respect that...nope.
Tigray options are now severely limited - because Turkish drones are doing heavy damage.
Ethiopia says Tigray attacked first. If that is true(I am not saying it is), then their actions would be consistent with the expected behavior of a modern government. If Abiy really believes what he says, then he is acting rationally.