And for a while, Srivijaya dominated trade in the region because there were so many ships going through the Strait of Malacca to and from China. But, as we will see in another episode, this trade abruptly declined in the 15th century, and with it, so did Srivijaya. This brings up a key point about Indian Ocean trade, which is that it was indispensable to the creation of certain city-states, like Srivijaya and the city-states of the Swahili coast. Without trade, those places wouldn't have existed, let alone become wealthy and grand. Trade was a huge source of wealth for these cities because they could tax it through import and export duties or port fees. But the fact that they are no longer powerful shows that trade can be a pretty weak foundation upon which to build a polity, even a small one. There are many reasons for this, like high taxes can motivate traders to find other routes, for instance.