About two-thirds of military deaths in World War I were in battle, unlike the conflicts that took place in the 19th century when the majority of deaths were due to disease. Improvements in medicine as well as the increased lethality of military weaponry were both factors in this development. Nevertheless disease, including the Spanish flu, still caused about one third of total military deaths for all belligerents. http://en.wikipedia.org/wiki/World_War_I_casualties#cite_note-population1971-29
Top 10 Bloodiest Battles of World War
World War I - There are many terrible battles, but this is a list of the worst.
http://www.toptenz.net/top-10-bloodiest-battles-of-world-war-i.php#ixzz1kkjlqfYg