World War I
Joseph Glidden (1813-1906) was a farmer who patented barbed wire, which revolutionized the American West and covered the battlefields of World War I. After seeing a demonstration of a type of wire to enclose large spaces for cattle ranching, Glidden perfected the invention and patented his Barb Wire in 1874. It quickly caught on and radically changed ranching in the West, allowing for much larger areas to be enclosed and many more cattle to be run. When he died in 1906, Glidden was one of the richest men in the country.
During World War I, both sides laid barbed wire by the mile in front of trenches to slow enemy attacks. The wire was so effective at stopping troops that it gave defenders a profound advantage in the war. In the early part of the war, nearly all large scale attacks featured massive artillery bombardments meant to cut the wire; however, due to its open construction, the wire was almost never cut. Glidden's invention—like Alfred Nobel's invention of TNT—was meant for peaceful purposes, but was adapted to kill millions.