Within hundred years of the advent of Islam, the Arabs had conquered vast areas in three continents from Sindh to Spain and Khorasan to Morocco. However, in spite of repeated campaigns they could not occupy the Kandahar-Ghazni-Kabul land route leading to the Khyber Pass - the strategic gateway to India. Two Hindu states of Zabul and Kabul (Southern Afghanistan) stubbornly defended their territory. The Arabs ceased to be a strong political power by 800 CE and their governors and the newly converted tribes started establishing their independent kingdoms in the far flung regions of the caliphate.