We've always needed a credit system to develop and maintain cities. I think the difference we've seen over the past several decades is that rather than being the site of industry, the city itself - the buildings, the infrastructure - has become an engine of capital accumulation. That means that the interests of investment capital are really focused on the built environment, and extracting as much capital from it, and buying and selling properties the way you would buy, sell and trade traditional commodities in generations past.