30 June

Events preceding British Declaration of War

 * 1914 Great Britain: Addresses in Parliament on the murdered Archduke: Lords Crewe and Lansdowne in House of Lords; Messrs. Asquith and Law in House of Commons.

Western Front

 * 1915 – Failure of German attacks at Bagatelle (Argonne) and Metzeral.
 * 1916 – Continued Allied bombardment on Western Front. French take Thiaumont.
 * 1917 – British capture further enemy defences south-west and west of Lens. German attack on Chemin des Dames. Violent artillery action west of Mort Homme (Verdun).
 * 1918 – Two air-raids on Paris. French success between Marne and Ourcq. German attack on British near Merris (River Lys) repulsed; British success north-west of Albert.

Eastern Front

 * 1915 – Germans cross Gnila Lipa line. Austro-German advance from Tomashov. Germans claim 150,650 prisoners in June.
 * 1917 – Heavy artillery action in Galicia.
 * 1918 – Murman Council decides to support Entente against Bolsheviks.

Southern Front

 * 1915 – Dardanelles: French take six lines of Turkish trenches. General Gouraud wounded, succeeded by General Bailloud.
 * 1918 – Italians capture Monte di Val Bello and Col del Rosso (Asiago). 2,000 prisoners.

Political

 * 1915 – Welsh miners' dispute settled. Changes in Russian Cabinet.
 * 1917 – Greece breaks off relations with Germany and Austria-Hungary.
 * 1917 – Soviet delegates leave Russia for Socialist conferences in Stockholm, England, France and Italy.

Naval and Overseas Operations

 * 1916 – Baltic: Indecisive small British naval action.
 * 1917 – German forces driven from Nyasaland to the Rovuma border by British and Portuguese.