Politics, Elections, & the Presidency: a Video Conversation with Thomas Jefferson
You once said “The lamentable resource of war is not authorized for evils of imagination, but for those actual injuries only, which would be more destructive of our wellness than war itself.” That was in 1801. A few years before, in 1794, you said “War is as much a punishment to the punisher as to the sufferer.” Is there an argument that you could endorse for launching a war to pre-empt “actual injuries?” To your mind, how certain of “actual injuries” in advance would the nation have to be to justify accepting the punishment of armed conflict?

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Answer:
This is a very good question. How are we to be certain what actual injuries are if they have not occurred? In fact, I have often said it is amongst the Decalogue of what I consider good common sense – how much pain un-occurred evil costs us. You are quite correct to proclaim war through the imagination of what could be evil is an unjust and in my mind illegal proclamation of war.

The only justification of war is in our self-defense, when we are attacked, as we were when I first took up the reins of office as chief magistrate, attacked once more, I might admit, by the Barbary pirates, who had attacked and terrorized our merchant shipping for many, many years, and it was tolerated in the administrations of President Washington and Adams but not so in mine. I called for a retaliation that we did not have to suffer for any further payment of tribute and that we might have to suffer future generations from being engaged the same. That was a direct attack upon our commerce and as well a retaliation a direct attack upon these Barbary kingdoms.

But beyond that, no, we could be afeard of the wars between France and England and try to protect and defend ourselves by going to war with either of the two, but I tried to prevent that with the imposition of an embargo and consider it successful in disallowing us to be engaged in those foreign politics.