John Robb on how small terrorist attacks can disrupt an entire system.

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.

(Sounds like the current credit crisis, doesn’t it? An seemingly minor number of subprime mortgages defaulted and that triggered the cascades of failure.)

But it’s not just terroist attacks like 9/11 that concern Robb, it’s the power of street gangs in cities like São Paulo and Rio de Janeiro, where they are powerful enough to challenge the authorities for dominance. He doesn’t see nukes being used as weapons because they are too difficult to build and conceal.

The result of a nuclear explosion in Moscow or New York would very probably be the annihilation of the country that manufactured the bomb, once its identity was determined—as it surely would be, since no plot of that size can remain secret for long.

We live in an increasingly dangerous world, Robb says, and the best way to defend ourselves is to decentralize all our systems. This builds in redundancy, makes cascading failures less likely to happen, and has the happy consequence of increasing participation by everyone as well as building genuine democracy and freedom.