The main precedent was the battle of Petersburg in the ACW, but the Europeans did not learn from it because they disrespected American military expertise. Trenches were still used in the 1930s (Spanish Civil War) but were rendered obsolete by mechanized transport (jeeps, tanks, planes). The Germans learned that, the French did not.
Yes, surprisingly, WWI was the first war in which more soldiers died from battle rather than disease and exposure. Machine guns and artillery were far more advanced than the mid-19th century wars. Numerous young men were unfortunately wounded by mustard gas, including one German corporal who was unfortunately not wounded enough.