When should Britain go to war?

There’s been a lot written this week about whether or not to fight the Islamic State in Iraq. This time the consensus among Spectator writers is that Britain should. There’s a clear moral case, but is it in our interests to go to war? The first time this question came up was in 1839 when China started confiscating opium from British traders. It may have been a good move to protect British trade, but the magazine was less convinced about the morality of it.

The perfect right of the Chinese authorities…to prohibit opium, will not bear disputing about; while the wisdom of their conduct in this matter—even supposing the object were to derive a revenue from home-grown opium—is at least as clear as that of the British Legislature, which forbids the growth of tobacco in Ireland in order to secure the tax on tobacco imported…If we have no trade with the Chinese but that which is maintained by arms, we shall have none at all.