This Chapter examines the American economy during World War II, with a particular focus on the emergence of computer technologies and its impact on financial markets. The Investment Company Act of 1940 originally sought to regulate “actively managed” mutual funds; soon, however, computer technology enabled a new financial product, the “passively managed” fund. Investment advisors increasingly were replaced by computers that managed and balanced funds more rapidly and efficiently. Computer-managed index funds that trade based on a static algorithms are not subject to the typical agency problems that arise when humans make decisions on behalf of others. However, algorithms may be subject to bias when their code is created by imperfect human beings. Software is only as good as its design. This technology spawned a host of new risks. Algorithms failed spectacularly in instances such as the Flash Crash. In response, regulators instituted new securities regulations, including Regulation NMS .Computers networked on the new internet helped the American economy recover from yet another financial crisis as public attitude towards corporations and “Trickle-Down Economics” began to sour.

This chapter focuses on financial markets and how these markets have enjoyed close ties to cities. It also demonstrates that social avalanches and tensional individuality have played a central role in how financial markets work and are conceived. I discuss this by examining the historical design of the trading floors of stock and commodity exchanges, introduced to avoid emergence within these exchanges of the avalanching of metropolitan life, as well as contrarian investment advice, which suggested techniques for how to avoid the avalanching properties of markets, techniques that ultimately subscribed to a tensional notion of individuality. The chapter also discusses more recent market developments such as the increasing computerisation of financial markets. I focus on the rise of algorithmic finance, in which fully automated computer algorithms are behind the majority of activity in financial markets. Through a discussion of the Flash Crash that took place in US markets in May 2010, I argue that fully automated algorithms may engage in social avalanching, meaning that sociality can indeed be ascribed to non-human algorithms.