Santa was very good to me in the books department. The first to be read was David Nicolle's Cross and Crescent in the Balkans.
This is the story of the Ottoman conquest of the Balkans. He covers the early history of the Ottomans and the chaotic world at the time. The decline of Byzantium, divided Islam and distracted European states all contributed to the extraordinary rise of this dynasty from a small tribe to superpower status.
This is not a simple narrative military history. The author gives a fair amount of social history that puts the Ottomans in context and explains their resilience. Not least the loyalty of Christian vassals in the Balkans. He also gives some detail of the Ottoman military and administrative system as well as their remarkable comeback after the defeat by Timur at Ankara in 1402.
The military history is outlined and expanded with a somewhat selective treatment of the major campaigns. The Crusade of Nikopol and the Siege of Constantinople get several chapters each. However, the battle of Maritsa plus the first and second battles of Kossova are virtually ignored. This is a bit disappointing as this prolific author has written detailed accounts of Nikopolis and Constantinople in the Osprey campaign series.
With that exception this is still a good overview of the period, written in the David Nicolle's very readable style.