Again, the conquest of Central Asia led her to overstep the barrier of the Kirghiz deserts. The wandering Kirghiz and Turkoman tribes of this barren region lived largely upon the pillage of caravans, and upon raids into neighbouring countries; they disposed of their spoil (which often included Russian captives) mainly in the bazars of Bokhara, Khiva, Samarkand and Khokand--Mahomedan Khanates which occupied the more fertile areas in the southern and south-eastern part of the desert region. The attempt to control the Turkoman raiders brought Russia into conflict with these outposts of Islam. Almost the whole of this region was conquered in a long series of campaigns between 1848 and 1876. These conquests (which covered an area 1200 miles from east to west and 600 miles from north to south) made Russia a great Mahomedan power. They also brought her into direct contact with Afghanistan. Russian agents were at work in Afghanistan from 1838 onwards. The shadow of her vast power, looming over Persia and the Persian Gulf on the one hand, and over the mountain frontiers of India on the other, naturally appeared highly menacing to Britain. It was the direct cause of the advance of the British power from the Indus over North-Western India, until it could rest upon the natural frontier of the mountains--an advance which took place mainly during the years 1839-49. And it formed the chief source of the undying suspicion of Russia which was the dominant note of British foreign policy throughout the period.