We know the Mongol Hordes did not have anything like Vattel and Martens.
We know the modern Russian army does (they were not roasting Georgians over an open spit for recreation a few months ago .... but they were using cluster bombs).
OK, now when did the change occur ? Before 1815 or after ?
What change(s) occurred .... what was "in bounds" and "out of bounds" 1805-1815 ? how did one know ?
We know that Vattel and Martens applies. Did Lieutenant Ivan Ivanovich Kusnetsov of the Tver Opolchenie ? Did Esaul Mehmet Ben-Haddad al Hadji of the Bashkir Host ? In 1812 or 1813 ?
[Note - I am try to de-nationalize this .... I don't think the issue was purely "bad" French vs. "good" Allies.]