What had the greatest effect on the rise of Islamism and nationalism in the Middle East?

Answer 1

It depends on who you ask, but most would say the influences of colonization on the Arabs and their relations with Europeans allowed for the development of an Arab national consciousness (in the same way that this had occurred in Europe).

The Arab National Consciousness developed along similar lines to the Greek National Consciousness which is to say that it was not primarily geographic (i.e. there would be areas where individuals would be Greek, but the majority not and vice versa and these areas were not necessarily contiguous), but it was a ethno-religious grouping. (If you spoke Greek and believed in Greek Orthodox Christianity, you were Greek. If you spoke Arabic and were Muslim, you were an Arab.)

Since Islam became part of the Arab identity, the result was that there were now two "solutions" to the Arab situation. Either that solution would come from the "Arabic" component (i.e. a secular government for ruling people based on their Arab-ness which led to Arabism, Pan-Arabism, Nasserism, etc.) or based on the "Muslim" component (i.e. a religious government for ruling people based on their Muslim-ness which led to National Islamism, Pan-Islamism, etc.).