Delete Without Reinstalling

Assume that the future battlefields are indeed in cyberspace.

If, for the sake of argument, Vladimir Putin could cut off the power supply to London at the touch of a button (resulting, yes, in some deaths, such as in hospitals or on the Tube), then why would he need a nuclear bomb?

And if, for the sake of argument, Theresa May could cut off the power supply to Moscow at the touch of a button, then why would she need a nuclear bomb, either?

In this age of cyberwarfare, nuclear weapons are obsolete.

If you can take down the power supply to London or Moscow merely by hacking into a computer, then who needs a nuke as a weapon, and what good is it as a deterrent?