There were so many deliberate civillian casualties that this went far beyond a war with insurgents. The Eritrean forces - who the government forces spent months denying were there - were also there to target Eritrean refugees (the regime is about as bad as North Korea).
Send peacekeeping troops?
You say that like you don't think it would have been a reasonable option?
As this crisis unfolded, there were many reasons a UN peacekeeping force would have been a good option.
Particularly as the racial rhetoric ramped up, NGOs reported systematic rapes of minority women, and the nationwide ethnicity-based detentions began.
We now have a famine situation due to all the deliberate targeting of civilian infrastructure and crops.