Over the past decade, the gravitational centre of contemporary conflict has shifted from the physical battlefield to the online battlespace, where the ingenuity of non-state actors has vexed governments and tested their militaries. Devising new architectures of participation, Al Qaeda and ISIS have weaponised social media and empowered their dispersed followers to organise, communicate and dominate the information domain.

Kevin Foster shows how conventional militaries in the US, Britain, Israel and Australia have responded to this challenge by...