Question

Describe the unique features that made World War I the deadliest conflict in history up to that

Answer 1

That was the first major war to use heavy machinery such as tanks, planes, shotguns, etc. and nations did not know how to counter these things. They were all still in old war mindsets where you March in lines for example, and by the time they figured out that they needed to change, many lives had already been lost. Not to mention trench warfare, where thousands of men threw themselves at the enemy just to gain a little bit of ground on them.