The Great War from 1914 to 1918 involved many major European powers and saw new weapons and tactics emerge. Fighting initially occurred mostly on the Western Front in trench warfare. Key battles included the First Battle of Ypres in 1914 which began the stalemate, and the battles of Verdun and the Somme in 1916 which resulted in massive casualties but no major gains for either side. New weapons like poison gas, tanks, aircraft, and submarines were introduced. The United States entered the war in 1917 on the side of the Allies after German attacks on merchant ships, helping ensure an Allied victory in 1918 as Germany ran out of troops and resources.

1. The Great War