Nuclear deterrent: 1651

As to the cavalier party, he was afraid both of assassination and other plottings from them. As to the former of these, he took a method that proved very effectual: he said often and openly, that in a war it was necessary to return upon any side all the violent things that any of the one side did to the other. This was done for preventing greater mischief, and for bringing men to fair war: therefore, he said, assassinations were such detestable things, that he would never begin them: but if any of the king's party should endeavour to assassinate him, and fail in it, he would make an assassinating war of it, and destroy the whole family: and he pretended he had instruments to execute it, whensoever he should give order for it. The terror of this was a better security to him than his guards.

--From History of his own Times--