One of the Horn of Africa's long-time scholars, Christopher Clapham, wrote "The Horn of Africa: State Formation and Decay" (2017), with Oxford University Press. A lot of the book, expectedly, focuses on Ethiopia. And, unfortunately for Clapham, the world of Ethiopia and the Horn has changed dramatically since. The book is accessible, which is often a nicer way to say this is not a detailed academic book for experts of the area but for students and/or generalists who might be interested to learn about the region. I am sure experts will read this book / have read this book, but may take away comparatively less (that said, a number of leading academics of the region have cited this book). I collected a few notes on ethnicity and on the Somali state, which are below:

"All ethnicities, nonetheless, are to some extent fluid, and this fluidity is encouraged in the societies of the northern highlands by the principle of bilateral descent. Whereas in most African cultures, to which lineage is characteristically extremely important, descent is traced primarily either through the male (patrilineal) or female (matrilineal) line, in this region each enjoyed a broadly equal status, and hereditary rights in land in particular could be claimed either through one's father or one's mother. This made it relatively easy to blur one's identity, by selectively emphasising the most advantageous line." (p. 13)

"The genie of ethnicity, however, once unleashed, could not be put back in its bottle. The assumption, derived from the TPLF's (and especially Meles Zenawi's) ideological commitment to Marxism, that ethnicity was no more than a superstructural phenomenon derived from economic exploitation, which could in turn be neutralised by representation and development, proved utterly inadequate. Instead, predictably enough, ethnic identities have become increasingly entrenched within a system that had been intended to nullify them. A new politics of identity has emerged, despite (and not least within) a hegemonic party that has become decreasingly able to control the forces of proliferation that it did not create (since these were already implicit in the mismatch between the state and its population), but which it had at least sought to manage." (p. 107)

"Somali societies have operated in the absence of formal government institutions in a way that could scarcely be conceived in the agricultural highlands of the Horn, where the breakdown of hierarchical control has been coterminous with violence. Nowhere is this clearer than in the operation of an economy that has functioned with remarkable efficiency despite the lack of overall political control, and has in the process spared many Somalis the levels of destitution that statelessness might have been expected to bring with it." (p. 149) 

Alex de Waal is one the world's most well versed scholars on East African politics, and has been intimately engaged with the region for decades. His 2015 book, "The Real Politics of the Horn of Africa: Money, War and the Business of Power," is essential reading for those interested in the region, or the intersection of politics and power broadly. Continuing the "thought provokers" series, a selection of quotes for this book follows, although highly recommended for full-length reading. 

On the political marketplace, de Waal argues the process:

• "…is fundamentally inhumane, reducing human beings to mere instruments and commodities, mutating public goods into private ones, and co-opting good intentions to achieve malign outcomes. We see politicians manipulating commendable policy goals such as state-building and peacekeeping as mechanisms to accumulate power and money, while perpetuating those same miseries that gave rise to those politics in the first place." (p. 4)
  

On the gendered political marketplace:

• "The political marketplace is gendered. The politicians in every chapter in this book are male. The social values and norms of a political marketplace are militarized and masculine. Those who rise in these political systems are those who can best mobilize money and deploy violence; not only men but men who are ruthless and inured to sentiment, who reduce human beings and human dignity to instruments and commodities. I do not develop a gender critique of the political marketplace in this book. However, the gendered nature of the business of power should be evident on every page." (p. 34)
  

On politicking and power:

• "After the government crackdown on opposition protesters, human rights organizations and western governments vigorously condemned Ethiopia. Meles was confident that his government would ride out the storm: the US would continue to support Ethiopia because of counter-terrorism, and the Europeans would speak harsh words but continue their aid because Ethiopia was a shining example of poverty reduction and progress towards the Millennium Development Goals. He was right." (p. 169)

• "In November 1989, SPLA and Ethiopian troops crossed the border at Kurmuk and were poised to take the town of Damazin, and the nearby Blue Nile dam that generated Khartoum's electricity supply. The Sudanese army was helpless – and was saved only by a secret commando action by the EPLF, which defeated the SPLA and the Ethiopians in January of 1990. In August of that year, President Bashir cautious alignment with Saudi Arabia was overruled by the leader of the Sudanese Islamists, Hassan al Turabi, who declared Sudan's support for the Iraqi invasion of Kuwait. This caused a deep financial crisis, and the Sudanese regime was saved only by the weakness of the SPLA – which collapsed after its sponsor, Menguistu, was overthrown – and remarkably creative political-business management" (p. 43-44).
  

On Somaliland:

• "Somaliland unilaterally declared independence from Somalia in May 1991 and set up a government that, more than two decades on, is functional but not internationally recognized. It has held a succession of competitive elections in which the loser has gracefully accepted his loss – including a presidential election in April 2003 that was decided by just eighty votes out of 675,000. The second-placed candidate, Ahmed Silanyo, gracefully ceded defeat to Dahir Kayin. Silanyo went on to win the 2010 elections by a handsome margin, and Kayin duly handed over power. Somaliland's political stability is an exception not only in Somalia but more widely in the region, and this small country of 3.5 million – a third of whom live in the capital city Hargaisa – has become the focus of a small but fascinating branch of comparative political science." (p. 130)