Geography
India is a large landmass about the size of Western Europe. It is a land of contrasts, featuring some of the wettest areas on earth as well as parts as dry as the most arid deserts. India is separated from the rest of the continent by a ring of high mountains- the Himalayas. This has acted as an unusually successful barrier to invasion. Only through the Northwest -- the location of the Khyber Pass -- could successful invasions of India be launched.
A major geographic feature is the great river valleys of the Indus and Ganges. In these fertile valleys, the earliest Indian civilization developed.