Trade/supply routes in Southeastern Asia

Islam arrive by way of Muslim merchants from Arabia and India. Since they pretty much controls the trade route to India and beyond conversion to Islam have obvious practical benefits. Malacca adopted Islam in 1445, and afterwards Islam quickly spread throughout maritime Southeast Asia.

Malacca as a state was founded around 1403 lasted just over a century until 1511 when the city was captured by the Portuguese. And since it controls both sides of the Strait of Malacca, it more or less effectively control trade to China, as well as the Spice Islands further to the east. After the Portuguese takeover Malacca fell into decline, partly due to poor Portuguese rule, partly due to competition from other ports (eg Ajeh and Johor, still in Malay hands, and much later British Penang and Singapore).