The Sufi community throughout the region proved crucial in the administration of the state. The Tariqa brotherhoods, most notably the Qadiriyya, to which every successive sultan of Sokoto was an adherent, provided a group linking the distinct emirates to the authority of the sultan. Scholars Burnham and Last claim that this Islamic scholarship community provided an "embryonic bureaucracy" which linked the cities throughout the Sokoto state. Economy After the establishment of the Caliphate, there were decades of economic growth throughout the region, particularly after a wave of revolts in 1816–1817. They had significant trade over the trans-Saharan routes. After the Fulani War, all land in the empire was declared waqf or owned by the entire community. However, the Sultan allocated land to individuals or families, as could an emir. Such land could be inherited by family members but could not be sold. Exchange was based largely on slaves, cowries or gold. Major crops produced included cotton, indigo, kola and shea nuts, grain, rice, tobacco, and onion. Slavery remained a large part of the economy, although its operation had changed with the end of the Atlantic slave trade. Slaves were gained through raiding and via markets as had operated earlier in West Africa. The founder of the Caliphate allowed slavery only for non-Muslims; slavery was viewed as a process to bring such peoples into the Muslim community. Around half of the Caliphate's population was enslaved in the 19th century. There was a huge expansion of slaves due to the jihad campaigns, frontier wars and slave raids. The expansion of agricultural plantations under the Caliphate was dependent on slave labor. These plantations were established around the ribats, and large areas of agricultural production took place around the cities of the empire. The institution of slavery was mediated by the lack of a racial barrier among the peoples, and by a complex and varying set of relations between owners and slaves, which included the right to accumulate property by working on their own plots, manumission, and the potential for slaves to convert and become members of the Islamic community. There are historical records of slaves reaching high levels of government and administration in the Sokoto Caliphate. Its commercial prosperity was also based on Islamic traditions, market integration, internal peace and an extensive export-trade network. Scholarship Islamic scholarship was a crucial aspect of the Caliphate from its founding. Sultan Usman dan Fodio, Sultan Muhammed