Kyiv’s Kherson offensive is not just about retaking territory but eroding Russian will to continue its futile and costly war. The great Prussian theorist of war, Carl von Clausewitz, took it for granted that defence was the strongest form of warfare, if only because a successful attack required superior numbers. For this reason the weaker side was obliged to defend. A state stuck on the defensive might prevent enemy gains but could not achieve its own objectives. They therefore had to use the time gained by the defence to create a more favourable balance of strength. Then they could strike....