The global conflict marked by trench warfare and the use of chemical weapons was World War I, which lasted from 1914 to 1918. This war was characterized by extensive trench systems, particularly along the Western Front, where soldiers faced horrendous conditions, stalemate, and high casualties due to static warfare. The conflict also witnessed the introduction of chemical weapons, like chlorine and mustard gas, which added a horrifying dimension to the battlefield. World War I fundamentally altered the political landscape of Europe, leading to the rise of new nations and ideologies, and it set the stage for many conflicts that followed in the 20th century.