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World War I killed more people more than 9 million soldiers, sailors, and flyers and another 5 million civilians involved more countries 28 and cost more money $186 billion in direct costs and another $151 billion in indirect costs than any previous war in history. It was the first war to use airplanes, tanks, long range artillery, submarines, and poison gas. It left at least 7 million men permanently disabled. It was a rapid spread after the assassination of the archduke.