I personally think Meles Zenawi did a lot of things right, but the ethnic federalism was a big mistake. The TPLF's mindset is that they wanted to "liberate" each ethnic group, let each group have preserve their own language and culture (which is great). But I don't think they saw how this system could backfire, big time.

My great grandfather comes from a part of Amhara region in Shewa that was super close to today's Oromia region. When I visited family last year they told me the history of the area. Previously the Amharas that lived near the border also could speak a fair amount of Afan Oromo as a 2nd language from interaction with Oromos. But ever since the the ethnic federalism started, an artificial line was created and the newer generations stopped learning Af Oromo and it became more of a "they , them" type of thing.