What were the new tools of war that caused such high rates of casualties?

World War I resulted in the creation of new military technology that changed warfare forever.

One of the most significant examples is the creation of the machine gun. This gun allowed a large amount of shots to be fired rapidly, causing an increase in the amount of casualties seen during World War I.

Another technology that resulted in large casualties was the introduction of chemical warfare. The used of chemicals like tear gas and mustard gas lead to several illnesses/casualties. This was the first war in which these chemicals were used on a massive scale.