Do you think Précis du droit des gens modernes de l'Europe was any more de Martens view of how states ought to conduct themselves than de Vattel's Le droit des gens, ou Principes de la loi naturelle, or were they both rather some kind of 18th/19th century wishful thinking by the respective individuals?
It certainly seems to me, and I'm open to correction here, that from 1812 onwards, no declaration of war was made by any party. Of course one could argue that Napoleon's invasion of Russia made any further declaration unnecessary. Prior to that time, declarations seem to be the norm. What changed?
As far as I can tell - rough dates - for the various coalitions (not at all sure about the status of these so-called coalitions) we have:
1st Coalition 1792: French declaration (written/verbal?) against Austria/Hungary 20 April 1792 (some modern sources state that the declaration was against Francis II specifically and I'd appreciate some help here - ie were declarations against individual heads of state or countries?)
2nd Coalition - 1798: The invasion of the Papal States by Naples seems to have been a trigger for just about everybody to join in a free-for-all. No declarations that I can see but happy to be corrected.
3rd Coalition 1805: No formal declarations that I can see, rather a drift to war as a result of a number of factors and more or less a resumption of the 2nd Coalition. British written ultimatum 10 May, verbal declaration on 18 May. Don't know about the others. As far as Britain is concerned this was to last until 1815.
4th Coalition 1806: Hardly a coalition in the sense of the previous ones in part because Britain was already at war with Prussia and France - Prussian unilateral declaration August (?) 1806. Not sure about Russia.
5th Coalition 1809: Again not really a coalition. Austrian letter of intent 11 April.
6th Coalition 1812: No declaration by anybody as far as I can see.
7th Coalition 1815: Personally I prefer '100 Days'. No declaration by anybody as far as I can see but apparently agreed by Congress on 13 March.
It seems to be very uneven and going out of fashion.
JC