There are many reasons for this, like high taxes can motivate traders to find other routes, for instance. But the main one is this. Reliance upon trade makes you especially vulnerable to the peaks and troughs in the global economy. The legacy of the merchant kingdom in Southeast Asia is still alive and well in Singapore, for instance. But one of the great lessons of cities that have declined or disappeared is that there's usually a town nearby that's eager to take your place and happy to offer lower taxes. It's almost as if the merchants decide where the people with the funny hats go, rather than the other way around. Thanks for watching.