According to John Robb in the summer edition of City Journal, as the majority of the earth huddles into cities for the first time in history, this concentration of people and the complex network of infrastructure it takes to make life liveable has empowered the likes of small groups to wreak havoc like never before.
This makes it easier, much easier, for terrorists and criminal supergangs to disrupt our lives by attacking the infrastructures necessary for modern urban dwelling such as electricity, water, transportation, even the police force itself.
...the networks of our global superinfrastructure are tightly “coupled”—so tightly interconnected, that is, that any change in one has a nearly instantaneous effect on the others. Attacking one network is like knocking over the first domino in a series: it leads to cascades of failure through a variety of connected networks, faster than human managers can respond.
This "coupled" superstructure makes it easy for terrorists and insurgents in Iraq to cripple the city's electricity system or for gangs like the First Command of the Capital in the slums of Sao Paulo, Brazil, to challenge the city's government for power by terrorizing the city with general anarchy.
Robb also believes the threat of small groups acquiring weapons of mass destruction is real to the networked cities of the 21st century. However, he thinks that the threat will not come from nuclear weapons or dirty bombs, but from a more unlikely source: biotechnology.
[T]he real long-term danger from small groups is the use of biotechnology to build weapons of mass destruction. In contrast with nuclear technology, biotech’s knowledge and tools are already widely dispersed—and their power is increasing exponentially.... In less than a decade, then, biotechnology will be ripe for the widespread development of weapons of mass destruction, and it fits the requirements of small-group warfare perfectly. It is small, inexpensive, and easy to manufacture in secret. Also, since dangerous biotechnology is based primarily on the manipulation of information, it will make rapid progress through the same kind of amateur tinkering that currently produces new computer viruses. Terrorists also have a growing advantage in delivering bioweapons. The increasing porousness of national borders, size of global megacities, and volume of air travel all mean that the delivery and percolation of bioweapons will be fast-moving and widespread—potentially on several continents at once.
Robb's solution to this apocalyptic picture he paints is decentralization. Decentralize services such as water and electricity to the borough level and smaller if possible to provide resilience against terrorists attacks on the infrastructure grid. Decentralize security to fight off gangs and give security forces a more military feel, which he notes is already happening. For instance, the use of SWAT Teams across the United States increased from 3,000 a year in the 1980s to 50,000 a year in 2006. Robb also foresees locally recruited or privately bought security forces to fight off small group terrorism and gang-related crime and chaos.
All politics is said to be local. Robb now argues all security should be too.
Our choice is simple: we can rely exclusively on our current security systems to stop the threats—and suffer the consequences when they don’t—or we can take measures to mitigate the impact of these threats by exerting local control over essential services.
For a similar argument, but not limited to cities, see Robert Kaplan's 1994 groundbreaking article, "The Coming Anarchy."