Unity of Somalis or unity of Somalia?
Who's to say that there aren't any unity in Somalia? The people of Somalia are centered around the Somali identity in one way or another, some by ethnicity, other by nationality, language etc. However, the majority of us (AKA ethnic Somalis) fall into all categories while minorities may not.
Also, this only applies to people who've live with us for a longer period of time, such as a Somali-Bantu who may not be ethnic, but are culturally, linguistically and nationally Somali. An immigrant, for instance, can not settle here and use nationality or language to claim kinship with us.
How's Somalia mentally weak? I'd understand Ethiopia considering how there are no majority ethnic group, but that doesn't apply in Somalia. Out biggest divisive factor is our clan based identities.