What neutral States would ever take up arms for the sole reason that, two Powers being at war, the 'laws of war' had been violated by one or both of the belligerents?
For offences of that sort there is no earthly judge.

Success can come only from the religious moral education of individuals and from the feeling of honour and sense of justice of commanders who enforce the law and conform to it so far as the exceptional circumstances of war permit.
"This being so, it is necessary to recognise also that increased humanity in the mode of making war has in reality followed upon the gradual softening of manners.

Only compare the horrors of the Thirty Years' War with the struggles of modern times.
"A great step has been made in our own day by the establishment of compulsory military service, which introduces the educated classes into armies.

The brutal and violent element is, of course, still there, but it is no longer alone, as once it was.

Again, Governments have two powerful means of preventing the worst kind of excesses--strict discipline maintained in time of peace, so that the soldier has become habituated to it, and care on the part of the department which provides for the subsistence of troops in the field.