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The British government’s forthcoming Strategic Defence and Security Review has a grand title, but threatens to achieve an outcome driven exclusively by the need to save money – £8bn ($12bn, €10bn) over four years. This is not unprecedented or even unusual. Economics rather than strategy persuaded Britain to withdraw from east of Suez in 1967.

Today, however, Britain’s armed forces are already so small that further cuts will leave them looking threadbare. One mooted National Security Council scenario would have cut troop numbers by 30,000. The army is thus expected to be grateful that the latest favoured variation, following last Thursday’s meeting, demands a loss of only 10,000.

A major difficulty is the lack of intellectual...