Slavery in India escalated during the Muslim domination of northern India after the 11th-century, after Muslim rulers re-introduced slavery to the Indian subcontinent. It became a predominant social institution with the enslavement of Hindus, along with the use of slaves in armies for conquest, a long-standing practice within Muslim kingdoms at the time. According to Muslim historians of the Delhi Sultanate and the Mughal Empire era, after the invasions of Hindu kingdoms, Indians were taken as slaves, with many exported to Central Asia and West Asia. Many slaves from the Horn of Africa were also imported into the Indian subcontinent to serve in the households of the powerful or the Muslim armies of the Deccan Sultanates and the Mughal Empire.