http://www.digitalhistory.uh.edu/historyonline/slav_fact.cfm
"The Arab and Islamic Slave Trade
1. Arabs were involved in the capture and transport of slaves northward across the Sahara desert and the Indian Ocean region into the Middle East, Persia, and the Indian subcontinent.
2. The trans-Saharan and Indian Ocean slave trade was much older than the transatlantic slave trade and continued into the 19th century.
3. As many African slaves may have crossed the Sahara Desert, the Red Sea, and the Indian Ocean as crossed the Atlantic.
4. An estimated 11,612,000 slaves crossed the Red Sea, Indian Ocean, and Sahara Desert from 650 to 1900, compared to 11,656,000 across the Atlantic from 1500 to 1900."