Stop the cycle of violence
The London bombings clearly illustrate that a war is going on. This war is fuelled on the one side by religious fanatics who use, really abuse, religion for their own misled conception of the world divided between the righteous and those outside the bounds of righteousness. Political and other differences with the non-righteous justify, in these fanatics' eyes, mounting massive attacks to specifically drive the point home to their adversaries that there is no geographic or time limit in the ongoing war.