This is the fourth volume in the Indian history series From Indus to Independence: A Trek through Indian History. Its title 'The Onslaught of Islam' is apt, since the book covers the initial period in which the newly founded religion of Islam started to move eastwards. Islam, almost immediately after its inception, had subdued large parts of the western regions of the Middle-East and stemmed the eastward movement of the Byzantine Empire. In ancient and medieval times all invaders of the Indian sub-continent came through the Khyber Pass in the Hindu Kush mountain ranges. The book examines the different invading armies starting with the Persian army of Darius the Great, the invasions of the Kushans and the White Huns, the repeated assaults by Mahmud of Ghazni 'The Hammer of the Idolaters', and the arrival of Muhammad of Ghur into the Indian sub-continent. While describing the military successes and failures of the Islamic armies the book also analyses the philosophical intermingling of cultural and religious ideas. This volume brings the narrative of Indian history to the establishment of the Delhi Sultanate.