At the time of the first world war there still seemed to be a general acceptance of protocols and procedures, although circumvention of same was well practised. Today I get sense of shoot first, apologise if you have to, second.
And the extent and range of the high powered weaponry today hasn't acted as a deterrent to fighting and nor did it then; although WWI was the first 'modern' weaponed war and peoples from all countries thought that alone should be sufficient reason not to go to war. Nope, there was too much 'honour' and 'face saving' at stake. Just like today, eh.
What I hadn't realised unti I read MacMillan was the size and reach of the Peace movement in the late 1890's and onwards. I thought that 'peace movements' were a modern invention - definitely not, they even had international conferences and brought the labour movements in as well. Even though ultimately they had no effect on the fact of the war they had been quite influential and served multi purposes locally, nationally and internationally. That cheered me.