"The existence of states," says Montesquieu, "is like that of man, and the
first have the right to make war for their proper preservation; the latter
have the right to kill in the case of natural defence. In the case of
natural defence I have the right to kill, since my life is my own, as the
life of him who attacks me belongs to himself. * * * From the right of war
follows that of conquest, which is the consequence: it ought then to
follow the spirit. * * * It is clear when the conquest is made, the
conqueror has no longer the right to kill, since he is no longer in the
position of natural defence, or for his proper preservation.
"That which has made them think thus (right to kill), is that they have
believed that the conqueror had the right to destroy society, whence they
have concluded that they had that to destroy the men who composed it,
which is a false consequence extracted from a false principle. Because the
society should perish, it does not follow that the men who form it ought
also to perish. Society is a union of men, and not men: the citizen can
perish and the man remain. From the right to kill in conquest, politics
have derived the right to enslave; but the consequence is as badly founded
as the principle."
There are certain rules that arise from the principle of
self-preservation, and form what Wolff calls "the voluntary law of
nations." "Hence it follows that all nations have a right to repel by
force what openly violates the law of the society which nature has
established among them, or that directly attacks the welfare and safety of
that society. At the same time care must be taken not to extend this law
to the prejudice of the liberty of nations."