northern India—in Rajasthan, the western Ganga basin, and Punjab—where
they built fortified villages and hilltop forts.
Horse-Riding Nomads from Afghanistan and Central Asia
                      CENTRAL ASIAN NOMADS
  The third group of warriors that propelled the medieval transition in India
  consisted of huge clans of Turkish, Afghan and Mongol horse-riding
  nomads, who dominated warrior society in the highlands of Afghanistan,
  Persia and Central Asia. They became the dominant military force in the
  lowlands after the tenth century. Mahmud of Ghazni’s father, Sabuktigin,
  fought Hindu Shahis in Punjab to acquire tribute to support his wars in
  Afghanistan and Persia.
     Mahmud succeeded his father in 997 and extended his patrimonial
ambition in all directions. He conquered Afghanistan and Persia, obtained the
title Yamin al-Daula (Right Hand of the State) from the Caliph, and took
tribute from local rulers in seventeen raids across India. Mahmud also used
some of his wealth to support Al-Biruni, the master geographer. Al-Biruni
had travelled trade routes documented for centuries by Arab geographers
whose knowledge had guided Mahmud’s expansion to the west and his raids
to the east and south. Al-Biruni’s geography locates places all across the
Indo-Ganga basin and the Indian Ocean coast, most importantly, Gujarat and
Sind. Rich Indian merchants in Ghazni would have been able to provide
Mahmud with intelligence on the most lucrative sites for military assault. By
Mahmud’s time, Indus and Ganga river basins were, like Rajasthan and
Gujarat, part of the trading world of Central Asia; and Mahmud brought them
into Central Asian politics as well.
Overemphasis on Political Fragmentation
The eleventh and twelfth centuries in Indian history are usually looked at