Barbed wire
More significantly, barbed wire was used extensively by all participating combatants in World War I to prevent movement, with deadly consequences. Barbed wire entanglements were placed in front of trenches to prevent direct charges on men below, increasingly leading to greater use of more advanced weapons such as high-powered machine guns and grenades. A feature of these entanglements was that the barbs were much closer together, often forming a continuous sequence.