Usman dan Fodio's jihad had created the largest empire in Africa since the fall of Songhai in 1591.

By the middle of the nineteenth century, when the Sokoto Caliphate will be at its greatest extent, it will stretch fifteen hundred kilometers from Dori in modern Burkina Faso to southern Adamawa in Cameroon and include Nupe lands, Ilorin in northern Yorubaland, and much of the Benue River valley.

In addition, Usman dan Fodio's jihad had provided the inspiration for a series of related holy wars in other parts of the savanna and Sahel far beyond Nigeria's borders that lead to the foundation of Islamic states in Senegal, Mali, Ivory Coast, Chad, Central African Republic, and Sudan.

An analogy has been drawn between Usman dan Fodio's jihad and the French Revolution in terms of its widespread impact.

Just as the French Revolution affects the course of European history in the nineteenth century, the Sokoto jihad affects the course of history throughout the savanna from Senegal to the Red Sea.

There will be thirty emirates and the capital district of Sokoto—which itself is a large and populous territory although not technically an emirate—by the middle of the nineteenth century in what is today Nigeria.

All the important Hausa emirates, including Kano, the wealthiest and most populous, are directly under Sokoto.

Adamawa, which had been established by Fulani forced to evacuate Borno, is geographically the biggest, stretching far to the south and east of its capital at Yola into modern Cameroon.

Ilorin, which becomes part of the caliphate in the 1830s, is initially the headquarters of the Oyo cavalry that had provided the backbone of the king's power.

An attempted coup d'etat by the general of the cavalry in 1817 had backfired when the cavalry itself revolted and pledged its allegiance to the Sokoto Caliphate.

The cavalry is largely composed of Muslim slaves from farther north, and they see in the jihad a justification for rebellion.

In the 1820s, Oyo had been torn asunder, and the defeated king and the warlords of the Oyo Mesi had retreated south to form new cities, including Ibadan, where they carry on their resistance to the Sokoto caliphate and fight among themselves as well.

Oyo, the great exporter of slaves in the eighteenth century, had collapsed in a civil war after 1817, and by the middle of the 1830s the whole of Yorubaland is swept up in these civil wars.

New centers of power—Ibadan, Abeokuta, Owo, and Warri—contest control of the trade routes and seek access to fresh supplies of slaves, which are important to repopulate the turbulent countryside.

At this time, the British withdraw from the slave trade and begin to blockade the coast.

The blockade requires some adjustments in the slave trade along the lagoons that stretch outward from Lagos, whereas the domestic market for slaves to be used as farm laborers and as porters to carry commodities to market easily absorbs the many captives that are a product of these wars.

War and slave raiding are complementary exercises among the Yoruba, who need capital to buy the firearms with which they fight in a vicious cycle of war and enslavement.

Military leaders are well aware of the connection between guns and enslavement.

Some of the emerging Yoruba states have started as war camps during the period of chaos in which Oyo breaks up and the Muslim revolutionaries who are allied to the caliphate conquer northern Yorubaland.

Ibadan, which will become the largest city in black Africa during the nineteenth century, owes its growth to the role it plays in the Oyo civil wars.

Ibadan 's omuogun (war boys) raid far afield for slaves and hold off the advance of the Fulani.

They also take advantage of Benin's isolation to seize the roads leading to the flourishing slave port at Lagos.

The threat that Ibadan will dominate Yorubaland alarms its rivals and inspires a military alliance led by the Egba city of Abeokuta.

Dahomey, to the west, further contributes to the insecurity by raiding deep into Yorubaland, the direction of raids depending upon its current alliances.

The Houses of Parliament in London had enacted legislation in 1807 prohibiting British subjects from participating in the slave trade.

Indirectly, this legislation is one of the reasons for the collapse of Oyo.

Britain had withdrawn from the slave trade while it was the major transporter of slaves to the Americas.

Furthermore, the French had been knocked out of the trade during the French Revolution beginning in 1789 and by the Napoleonic wars of the first fifteen years of the nineteenth century.

Between them, the French and the British had purchased a majority of the slaves sold from the ports of Oyo.

The commercial uncertainty that followed the disappearance of the major purchasers of slaves had unsettled the economy of Oyo.

Ironically, the political troubles in Oyo had come to a head after 1817, when the transatlantic market for slaves had once again boomed.

Rather than supplying slaves from other areas, however, Oyo itself had become the source of slaves.

British legislation forbids ships under British registry to engage in the slave trade, but the restriction is applied generally to all flags and is intended to shut down all traffic in slaves coming out of West African ports.

Other countries more or less hesitantly follow the British lead.

The United States, for example, had also prohibited the slave trade in 1807 (Denmark actually was the first country to declare the trade illegal in 1792).

Attitudes change slowly, however, and not all countries cooperate in controlling the activity of their merchant ships.

American ships, for instance, are notorious for evading the prohibition and going unpunished under United States law.

It should be noted, moreover, that the abolition movement had concentrated on the transatlantic trade for more than five decades before eventually turning to a full-fledged attack on slave trading within Africa itself

The Royal Navy maintains a prevention squadron to blockade the coast, and a permanent station is established at the Spanish colony of Fernando Po, off the Nigerian coast, and given responsibility for patrolling the West African coast.

For several decades, as many as one-sixth of all British warships will be assigned to this mission, and a squadron will be maintained at Fernando Po from 1827 until 1844.

Slaves rescued at sea are usually taken to Sierra Leone, where they are released.

British naval crews are permitted to divide prize money from the sale of captured slave ships.

Apprehended slave runners are tried by naval courts and are liable to capital punishment if found guilty.

A lively slave trade to the Americas will nonetheless continue into the 1860s.

The demands of Cuba and Brazil are met by a flood of captives taken in wars among the Yoruba and shipped from Lagos, and the Aro continue to supply the delta ports with slave exports through the 1830s.

Despite the British blockade, almost one million slaves will be exported from Nigeria in the nineteenth century.

The risk involved in running the British blockade obviously makes profits all the greater on delivery.

The campaign to eradicate the slave trade and substitute for it trade in other commodities will increasingly result in British intervention in the internal affairs of the Nigerian region during the nineteenth century and ultimately lead to the decision to assume jurisdiction over the coastal area.

Suppression of the slave trade and issues related to slavery will remain at the forefront of British dealings with local states and societies for the rest of the nineteenth century and even into the twentieth century.

Initial attempts to open trade with the interior by way of the Niger cannot overcome climate and disease, which takes the lives of a third of a British riverine expedition in 1842.

Use of quinine to combat malaria on similar expeditions in the 1850s will enable a Liverpool merchant, Macgregor Laird, to open the river.

Laird's efforts will be stimulated by the detailed reports of a pioneer German explorer, Heinrich Barth, who travels through much of Borno and the Sokoto Caliphate and records information about the region's geography, economy, and inhabitants.