Which innovation made WWI casualties higher than any other previous war?

Trench warfare placed soldiers in fortified positions facing one another across exposed ground. New weapons such as machine guns and heavy artillery made attacks across that ground extremely deadly, while the trenches kept armies fighting for long periods. Radar was not invented until decades later, and alliances helped expand the war but were not the innovation that made battlefield casualties so high. The correct choice is “a new defensive tactic known as trench warfare.”

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