Final little extract from Power and Plenty:
...France banned imports of many British goods and in October 1793 she banned all British manufactures. Meanwhile, the British blockaded the French coast. As Eli Heckscher emphasized, measures of this kind were motivated by mercantilist reasoning, and in particular the desire to prevent the enemy from earning precious metals via exports.
As they point out, by the wars of the Twentieth century even the politicians had grasped the point that is imports which are the desirable items, exports simply the boring things that have to be done to pay for them. But that earlier gross misunderstanding of the whole point of trade did lead to some near insane actions:
...in 1810, when Britain was suffering from a poor harvest but France had food in abundance, Napoleon authorized food exports to its enemy accounting for roughly 13% of English grain consumption of that year. Such a policy stance, based on the hope that one's opponent could be brought to its knees by supplying it with food in return for gold...
Well, the authors are too polite to go on to describe it as ludicrous but that's certainly how it appears to me.
Fortunately the politicians of our own day have grasped at least part of this point: now all we need to do is to get them to understand that you cannot tax us into prosperity...and the CAP...and the CFP...and markets in education...and health...well, quite lot of things actually.