Adal was a Muslim Sultanate, it’s borders corresponding with the territory of modern-day Somalia. In 1529 they invaded Christian Ethiopia, and little by little the Ethiopians were driven back and on the verge of defeat, until the Portuguese (already with a presence in the Indian Ocean) stepped in to support their fellow Christians in the war against Islam and the Ottoman Empire with a small army that punched well above its weight in the battles to come.
In addition to an interesting account of the key players, the armies, campaigns and battles, we get a good bit of background into the region and it’s diverse peoples. It is clearly well researched and illustrated throughout with maps and contemporary illustrations.
For something a little different I can recommend this book highly, and I guess it has a fair bit of wargaming potential for those who like to collect figures and game the the more fringe conflicts.