A slave woman's status was usually denned as "domestic". Seeking slave women through force or purchase was considered worthwhile both to increase reproductive capacity and, especially in matrilineal societies, to strengthen the father's line—the children of a female slave belonging without question to the father's family. In the nineteenth century, central and south-central Africa especially experienced unprecedented growth in the slave trade with the Indian Ocean in exchange for increasingly sought-after firearms and Western manufactured products imported by Arab and Swahili traders. Whatever has been written about them in the past, African women's condition was hard in the nineteenth century, perhaps even harder than it had been before because of the political and social disturbances inside Africa. Sahelian ranked societies were hostile to mixed marriages. There a slave was at most a concubine. Besides, slaves produced fewer children than free women because of their servile status.