Not to mention the introduction of the Gatling gun. It's been written many times that the general staffs of the European militaries would have been well served to study the US civil war in much greater detail than they apparently did. A bayonet charge at Gettysburg? Disaster. A bayonet charge at the Marne? Fucking suicide. Yet they still tried. I guess they felt they had to do something, and the tank wasn't deployed until the latter years of the war.
Yep and WW1 increased the strength of the defense yet again with the introduction of cordite which was a smokeless powder, before that you had all these guys firing and the thick smoke would drop visibility to only a few meters very quickly. In WW1 they could fire repeated volleys with good visibility, the only reasonable response for the attacking army was to burrow below the hail of accurate fire into shallow foxholes that expanded and expanded to become the miles of trenches. That in itself was interesting as in the very early stages the trenches were straight which meant that a small force that managed to take part of the trench could use enfilading fire along the trench and wipeout huge numbers of enemy troops. So after a while they started building these zig zag ones: