What i am trying to say: When societies accepted new rulers it often reflected their preference for systems offering more stability, freedom, and prosperity. Societies embraced islamic rule (and kept their own language and religion for centuries) for its ability to give rhem a better life.

While the religious aspect of Islamic expansion is often emphasized, the technical aspects are neglected. Islam was not solely a religious phenomenon but also a socio-economic transformation driven by practical benefits.

Regarding the question of whether "people become reasonable on their own," I believe that external catalysts are almost always necessary to inspire change and shift attitudes. Societies that remain closed off and resistant to outside influences are often the first to stagnate and decay.