Today is another aniversary from 100 years ago - the Sinking of the Lusitania. The Lusitania was a British passenger liner running between New York and Liverpool, still making runs in 1915, despite the increased danger from German submarines. The Germans wee. at this point in the war, beginning to carry out unlimited submarine warfare - that is, they were beginning to attack British ships on sight, from under water, with torpedoes - rather than surfacing and attempting to evacuate the ships first. They made no secret of this - before the Lusitania left New York, they circulated a warning, pointing out that England was a war zone, and they had the right to attack ships near England, and would - that passengers traveled at their own risks. But passengers traveled, including a lot of Americans - and when the Germans sank it, 218 Americans died, of the 1198 total casualties. It caused a sensation - the British condemned the attack roundly; the Americans too, and edged toward war - and certainly turned against the Germans. The Germans, for their part, while defending their actions, abandoned unlimited submarine warfare for two years - they only resumed in in 1917, when the war was starting to go against them. It didn't help - in 1917, the Americans were having none of it, and came into the war not long after. The sinking of the Lusitania, then, did finally lose the war for Germany (the US's involvement went far toward breaking the stalemate) - though it took a few years to come to pass.
That is probably all for the best, but you have to feel some sympathy for them. They claimed at the time that the Lusitania was a legitimate target, carrying armaments - and it was. Which makes it not entirely untrue to say that the passengers were being used as human shields - the morality gets muddy there. The morality of naval warfare - blockades and submarine warfare - is pretty murky anyway. The British blockades the Germans for the whole war - and went a long way toward starving them out. Causing serious ongoing suffering in the civilian population. But the British did this with surface ships - they had a huge navy that could cut off trade with Germany without using submarines. The Germans lacked the surface fleet, but they had submarines, which were very effective against shipping - though the nature of submarine warfare makes it impossible to wage without killing people. Surface ships can turn back freighters - a large surface navy can stop shipping without always sinking it, can drive off any military escorts and so on - submarines can't do that. They can only sink ships. They can't surface to engage with ships - a few destroyers can rout a submarine. So waging a blockade with subs is a murderous affair - immediately murderous: killing people instantly and terrifyingly, rather than starving them slowly, the British way.
But it points to something else - that 20th century warfare was becoming total war - wars are always won and lost through logistics, but this is all the more obvious in the 20th century, with heavy industrialization, with larger populations, concentrated in cities that have to bring their food from somewhere else. And with the industrialization of warfare itself, creating an insatiable appetite for machines of killing. Commerce becomes all the more important - commerce and industry - and they become legitimate targets for attack, with all the civilian casualties that come with it. This would only grow more important as time passed, as air power became more important - it would justify the use of strategic bombing in WWII. That's a topic for another day - but in the end, it would end up killing millions (maybe) of civilians, without really making any dent in anyone's war making capabilities. Not in absolute terms, and not in comparison with what submarines (and conventional blockades) would accomplish.
Finally - here is Winsor McKay's animated film on the sinking of the Lusitania, a fine piece of wartime propaganda by a great filmmaker: