Was the Kaiser right to trust the word of Captain Campbell? Of course he was. "The young soldier returned to his family home in Gravesend, Kent, in December 1916 and spent time with his mother before returning to the camp, where he was held until the war ended in 1918."
I said "only in the past" but I suspect the same would happen today if two countries were fighting.who regarded each other as basically civilised, with some fundamentally shared notions of culture and honour. That was pretty common for European wars up to WWI. That Sweet Enemy, which I have plugged before, gives numerous examples of the links between Britain and France even during the Napoleonic Wars. Some remnants of that mutual respect were found even in the European combatants in WWII, which was to a large extent regarded, perhaps on both sides, as a fight of civilisation against barbarism.
But since then, war has been viewed (at least in the western world) as something that 'we' do to people who do not share a common civilisation. Korea, Vietnam, Iraq and Afghanistan are all quite foreign to the Brits, Americans and French. (The Falklands conflict hardly counts.) In some ways that is the price of progress: democracies do not fight democracies and so on. But it is a price: we lose a certain empathy for our opponents and an ability to fight with regard to certain standards of decency.
Let us take an example: drone warfare. "Mr. Obama ... in effect counts all military-age males in a strike zone as combatants", the New York Times tells us. One cannot imagine that the British or the Germans would have taken that approach during WWI (certainly not prior to universal male conscription, which at least provides some support for it). Of course, that is partly a problem caused Al Qaeda being a non-uniformed, irregular opposition: it is simply much harder to distinguish combatants from non-combatants. But it is also, I suspect, a problem deriving from the opponents not sharing a common culture.
The Atlantic has an interesting article about drones, including describing what a drone controller actually does: "flying a drone, [the remote pilot] sees the carnage close-up, in real time—the blood and severed body parts, the arrival of emergency responders, the anguish of friends and family. Often he’s been watching the people he kills for a long time before pulling the trigger. Drone pilots become familiar with their victims. They see them in the ordinary rhythms of their lives—with their wives and friends, with their children."
The inter-European wars were not just wars between combatants who shared a common culture, but also in some ways reciprocal. If you were on the same side as the Prussians this year and might be captured by the French next year, but could be on the victorious side against the Austrians the year after, then you all had an interest in playing by the same basic rules. But who imagines that the Afghans might be sending drones to hover over Washington, their controllers gradually trying to work out who is a threat and who is just a secretary? And if that could happen, what rules would we want to play by? Under the rules of war espoused by the Americans, as I understand them, an Al Qaeda operative is entitled to fly a remote controlled aircraft around America, following Barack Obama around his house and on holiday, looking in through his windows as he kisses his children goodnight or reads a book on the loo, and then to make it fire a missile at his car and count his security detail as combatants. Such a drone controller would simply be a latter day Red Baron, a knight of the sky with a more comfortable chair and better working hours.