Complex sentence: It is also known that some of the earliest Southeast Asian Islamic sultanates--such as Samudra Pasai--were first established in Aceh, which means Islam first arrived in Aceh before spreading throughout Southeast Asia.
Split into simpler sentences: It is also known that some of the earliest Southeast Asian Islamic sultanates--such as Samudra Pasai--were first established in Aceh. This suggests Islam first arrived in Aceh before spreading throughout Southeast Asia.