On taking things from parties who are not at war

It might seem superfluous for us to speak of those who are not involved in war, since it is quite clear that no right of war is valid against them. But since in time of war, on the pretext of necessity, many things are done at the expense of those who are at peace, especially if they are neighbours, we must briefly repeat here what we have said elsewhere, that the necessity which gives any right over another's property must be extreme; furthermore, that it is requisite that the owner himself should not be confronted with an equal necessity; that, even in case there is no doubt as to the necessity, more is not to be taken than the necessity demands. [T]hat is, if retention is sufficient, then the use of a thing is not to be assumed; if the use is sufficient, then not the consumption; if consumption is necessary, the value of the thing must then be repaid.

The duty of those at peace towards belligerents

On the other hand, it is the duty of those who keep out of a war to do nothing whereby he who supports a wicked cause may be rendered more powerful, or whereby the movements of him who wages a just war may be hampered, according to what we have said above. In a doubtful matter, however, those at peace should show themselves impartial to either side in permitting transit, in furnishing supplies to troops, and in not assisting those under siege.