Nice crusade you are leading.
I am not overly interested in either praising nor damning the régimes of the past. I am more interested in knowing what happened.
However, since the search function on the Forum is not exactly its greatest advantage, could you please indicate where the French or the Russian governments ever accepted the principles of either Vattel, Martens or any similar writer that codified a limitation on a autocrat's methods of waging war ?
Thanks.
A generalization such as "civilized nations agreed" leaves me very cold in terms of assessing individual actions. The application of laws, especially under any anglo-american conception of such, requires the "guilty" to have formed the intent to commit a crime, and that a crime be identifiable as such in advance of its commission.
There are many "reformers" today whose ideas might be national or international law in the future. Simple example : Russia and the USA have cluster munitions, and refuse to sign international conventions banning their use. One supposes that their use is already a war crime in several nations, and may become one in the USA or Russia in the future. But this year, if one dropped a cluster bomb in Georgia or Afghanistan, you were not a (war) criminal merely for having used this weapon.