Austen begins with the history of the region down to the Arab conquests and the arrival of Islam. He draws on climate history, archaeology, and sources such as Herodotus to touch on the farming civilization of the Garamantes ("more likely the precursors of [Islamic-era trans-Saharan trade] than its pioneers"), the Berbers, and the Romans and Byzantines. Mindful of the limitations of negative evidence, he concludes that "the camel did not arrive on the Mediterranean coast of Africa much before the first century BCE" and "before the Arab conquests of the seventh century CE, we have no clear indication of caravan traffic linking the Sudanic and Mediterranean neighbors of the Sahara". Dissident Muslims, Kharijite groups such as the Ibadis and Sufris, were the first to organize regular trans-Saharan trade.
There was little technological change over the next millennium but "the caravan system did become more efficient during the many centuries in which it flourished, in terms not of transport technology but business relations and desert politics". A caravan might consist of thousands of camels and hundreds of people, managed by a professional leader. The economics of trade across the Sahara changed with the commodities involved: gold, slaves, and ivory, but also textiles and leather goods and cowrie shells. Austen gives a feel here for the diversity of peoples and languages and networks involved, and for the impact of alternative sea routes via West Africa (not always significant before 1850: the Atlantic and Saharan slave trades, for example, had "largely complementary gender demands").
Austen's treatment of the political history has more on Sudanic Africa and less on North Africa, offering a broad, semi-narrative account of the empires and kingdoms of Ghana, Mali, the Almoravids, Songhay, Kanem, and Sokoto, among others. Islam played a central role in the later part of this history, when empires were built by jihadist clerical leaders such as Usman dan Fodio and Umar Tal. There's a bit about military technology, taxation, the constraints on state power, and so forth, but the record is "rich in the drama of conflicts and personalities, yet somewhat disappointing with regard to how civil governments operated".
Turning to Islam more broadly, Austen looks at the spread of scholarship ("Muslim scholars recruited from within local ethnic groups began to appear in the major commercial centers of the Sudan and southern Sahara from about the thirteenth century") and sectarian divisions. Early Shiite and Kharijite trends shifted to a Sunnism dominated by a strict North African Malikism but with a strong Sufi strand: tariqa such as the Sanusiyya came to dominate much of the Sahara. The forest zones of West Africa, where few rulers were Muslim, had different traditions. Suwarianism, for example, stressed links to the broader Islamic world and separation from traditional beliefs, but focused on the Sufi idea of batin or concealed religious knowledge, producing a kind of "orthodox syncretism".
Austen also covers what he calls "Islamicate culture", in regions and traditions "dominated, but not totally defined, by Islam". He touches on Judaism, Ibn Khaldun and Ibn Battuta, and architecture and the decorative arts. But the focus is on the southern spread of Arabic and on the use of Arabic script for local languages, notably in the development of Berber, Mande and Fulani literature, built on existing traditions of chronicle and poetry.
In a final chapter on the effects of European colonialism, Austen eschews any attempt at a general history, and doesn't cover events after the mid-twentieth century at all. He emphasizes the limited power of early regimes and the limited extent of economic realignment towards the Atlantic. And he looks at colonial relationships with Islam, in religious policy but also in education: "However tolerant and even supportive colonial authorities may have been to Islam as a religion, they also represented a secular Western culture that threatened to displace the Islamic Mediterranean as the reference point for Africans seeking their place in a wider world."