which of these historical factors contibuted to Indonesia having the largest muslim population of any nation in the world

Indian trade

Explanation:

We don´t have a categoric knowledge about the origins of Islam in Indonesia, but according to historical evidence available, it seems that trade played a major role in the arrival of Islam in Indonesia in the 13th century. Two Muslim trading kingdoms existed in northern Sumatra, Samudra-Pasai and Perlak by then. At Samudra-Pasai, there´s a royal tomb completely inscribed in Arabic dated 1297. Further developments in the region also point at an expansion of trade with India and in the Indian Ocean as a major factor in the spreading of Islam in Indonesia.

this is a good question! i'll do some research and come back when i have the answer!