The military conflict known for shell shock, trench warfare, and wide-scale devastation is World War I. Lasting from 1914 to 1918, the war was marked by brutal trench battles that created a deadly stalemate on the Western Front. The psychological impact, including "shell shock," reflected the severe mental toll of warfare on soldiers. World War I's unprecedented scale of loss and destruction led to significant political changes globally, setting the stage for future conflicts and reshaping international relations in the 20th century.