During the First World War, the warring parties tried everything they could think of to win. The German army was the first to use deadly poison gas on the Belgian battlefields.
On 22 April 1915, French troops saw a yellow-green cloud of chlorine gas coming towards them. Within ten minutes, thousands of soldiers had choked to death. The German attack violated international agreements that prohibited the use of poison gas. Afterwards, the French and English also resorted to the use of poison gas.