I'm only really qualified to talk about Somali history, but
@twistedirregular is on point as far as the Ogaden War. The Ethiopian army was in a very sorry state at the time that Barre rolls in to take back the Ogaden, but more importantly, the Somali Army was one of the most fearsome in Africa. I'll repost a block of text I wrote in another thread:
In an average war (if there is such a thing) between East African nations, I don't think there's all that much that could have overextended the Somali Army except an OTL Ogaden War scenario where one world superpower throws significant weight on the other side. The Somali Army, which had been getting anywhere from 55 million to 83 million dollars worth of funding yearly from the Soviets by this time, had 6 tank battalions, 11 artillery battalions, 9 mechanised infantry battalions, 2 commando battalions, and 5 infantry battalions according to the British think tank IISS in 1977. The Italians estimated that the Somali Army actually had 12 artillery battalions, 7 infantry battalions, 3 commando battalions, 9 mechanized infantry battalions, and 7 tank battalions. The Somali Army was the largest mechanized force on the continent at the time - during the invasion it sent out anywhere from 250-310 tanks, 20-30 of which were T-55s and 15 of which were
T-62s. These statistics aren't scary compared to what Warsaw Pact and NATO members could field, but in the context of Africa circa 1977 where countries often struggled to field 30 working WW2-era tanks, this was absolutely
terrifying.
Without massive Warsaw Pact or NATO saving, the Ogaden is as good as gone.