We know where this is likely to end. We will accept Russia's sovereignty over Crimea. Sanctions will be quietly dismantled, Moscow will reassure Kiev with a deal on neutrality. Nato will agree no further eastward expansion. The G7 will again become G8; and Crimea will join Tibet, Kosovo, East Timor, Chechnya, Georgia and other territorial interventions which history students will struggle to remember. But how do we get from here to there?... Crimea must be a classic instance of a great power wrestling inside the shrunken straitjacket of imperial retreat, as Britain did, far more violently, half a century ago....