The first conclusion to be drawn from the foregoing analysis is that ecology was a major factor determining the progress and character of the Islamic… - André Wink

It is in this direction, probably, that we have to look for an answer to the question why Buddhism disappeared, in the eleventh to thirteenth centuries, from its homeland in the South-Asian subcontinent, while being successfully disseminated to the peasant societies of mainland Southeast Asia. When one turns to the secondary literature on Buddhism one finds mere hints of an explanation of this issue. If it is addressed somewhat more systematically, it usually amounts to one or another version of the theory that since Buddhism at one time prevailed only in those areas which later converted to Islam, and since there are no Buddhists left in these areas, we must deduce that the Buddhists converted to Islam. Thus it is most often observed that Buddhism disappeared from those parts of South and Southeast Asia which were overrun by Muslim armies in the medieval period and hence-forward became subject to Islamic rule. Mass conversion of Buddhists to Islam in Sind and Bengal, it is then alleged, occurred due to political pressure or because Buddhists saw in Islam a means to escape from the Hindu caste system and brahmanical oppression. This, we are told, is also the reason why Buddhism survived in areas which did not suffer the largely 'destructive' Islamic impact: the Himalayas and beyond, Sri Lanka, mainland Southeast Asia (but not Indonesia, which was conquered by indigenous Islamic rulers).

By the time that the Turko-Islamic conquerors arrived in North India, in the eleventh to thirteenth centuries, Buddhism was no longer a religion of a floating population of itinerant monks but had become institutionalized in monasteries, which, supported by royal endowments of land as well as by donations from the mercantile communities, tended to become large academically oriented centres with permanent residents, vulnerable to outside attack, but still aloof from the rural masses (which only adopted random cultic elements from the religion). What happened, then, during the Islamic conquest, is that the academic (and soteriological / philosophical) tradition of Buddhism was uprooted in India itself, but replaced, outside the orbit of Muslim rule, by a variety of regional forms of Buddhism.

In summary, we find an interrelated set of significant changes occurr­ing in the eleventh and twelfth centuries on a global scale. With the rise of Europe, the expansion of Islam into North India, and the upsurge of China, the economic supremacy of the Middle-Eastern caliphate was gradually reduced.