The arrival of global guerrillas -- small groups that can successfully fight wars against states -- is merely the first expression of a much larger trend line. The larger trend is a radical improvement in the productivity of warfare through the use of mechanisms outside of the control of the state. Since there have been no strides in eliminating the drivers of warfare at the small group level (in fact, just the opposite has happened) and our core systems remain hopelessly concentrated/interconnected, the use of this newly emergent productivity is inevitable.
If we follow this trend line, the path in development is clear. First, over the next decade or two, the size of the group necessary for global warfare will continue to decrease and decentralize (through a near term shift to systems disruption and open source organizational forms). Second, we will eventually reach a point when the weaponry available to these groups will enable them to initiate a catastrophic black swan (an event that is impossible to predict).
RAND's Charles Meade and Roger Molander provide a great example of a catastrophic black swan in their contemplation of the effects of the explosion of a nuclear bomb, smuggled in a shipping container, at the port of Long Beach CA (PDF). Of particular interest are the cascading effects of such an attack -- such as port closures across the US, which would result the immediate economic isolation of the US for an indeterminate duration. Of course, viewed within the context of a catastrophe like this, it is important to consider the first expression of this trend line (global terrorism using conventional weaponry) as a grace period. History has given us an opportunity to get security right before the next wave hits. So far, it doesn't look like we have learned anything at all.