In what ways did world war 1 represent a frightening new kind of warefare?

The trench warfare and gas attacks.

Explanation:

During WW1, there were trenches dug up by the soldiers. Any land between the trenches was called no man's land. This is because Bullets, gas bombs, and all sorts of new weaponry was being used into overdrive. The gas, as I was referring to, was extremely toxic and dangerous. An example would be the mustard gas - tasteless, odorless, and colorless, it was virtually unidentifiable at the time. It could seep through the clothes and armor, cause blisters and severe burns, and make you very sick. Men had to get amputations because of the wounds and infection caused by the gas.