The reason for their attack on Joorey? Well, the Makaahiils in Ogadenia had looted thousands of camels from Cawlyahan in Afdheer. The reason was Makaahiil made up the single biggest OG clan in Darwiish forces and when the Dervished were defeated, Makaahiil came back home in Doollo(Wardheer) with nothing. They literally had nothing. After looting few hundred camels from neighboring clans, their biggest feat of camels came when they stole thousands of camels from Cawlyahan in Afdheer region.
Rather than go after the Ogadenia Makaahiils, the Cawlyahans unleashed on the cattle-heading and peaceful Reer Joorey Makaahiil. The Makaahiils initially defeated the offending Cawlyahans but then second time the Cawlyahans came back with big machines looted from the British and almost defeated the Maakaahiil and were able to secure couple of thousands of cattle.
http://muse.jhu.edu/article/23692


from being the strongest Ogaden to being the weakest of all.