Europe 1915: Central Power Breakthrough in the East
7 May 1915German submarine
sinks Lusitania with
angering US and
to stop unrestricted
Italy joined the Allies in May, but the rest of the year favored the Central Powers. In August the Germans pushed the Russians out of Poland, while in October the Bulgarians joined the War and helped defeat Serbia. The Allies landed in officially neutral Greece in an attempt to save the Serbs, but were only able to rescue part of their fleeing army.
1 May–18 Sep 1915 Gorlice-Tarnow Offensive▲
Germany overruns Poland and Lithuania
7 May 1915 Sinking of the RMS Lusitania▲
German submarine U-20 torpedoed the RMS Lusitania in the North Atlantic Ocean off the southwest coast of Ireland, sinking her. The action killed 1,198 of the 1,959 people aboard, including 128 of 139 American passengers. Although she was a British ship carrying munitions and the German Embassy in Washington had issued a warning implying that she might be attacked, the sinking shocked the United States and helped galvanize opinion against Germany. In response, on 9 September 1915, Germany ordered the restriction of U-boat attacks to ships that were confirmed to be British, with no actions against passenger liners permitted at all.
23 May 1915 Italian entry into WWI▲
Following the secret promises of territory made by the Allies in the Treaty of London, the Kingdom of Italy declared war on Austria-Hungary, entering World War I on the side of the Allies. This act occurred only 19 days after Italy's denouncement of its membership in the Triple Alliance with Austria-Hungary and Germany.
3 Oct 1915 Macedonian Front▲
Allies land at Salonika in Greece
8–9 Oct 1915 Austria-Hungary and Germany capture Belgrade▲
Austria-Hungary and Germany capture Belgrade
14 Oct 1915 Bulgaria's entry into WWI▲
The Kingdom of Bulgaria declared war on the Kingdom of Serbia, bringing Bulgaria into World War I on the side of the Central Powers. Its entry both doomed Serbia - by creating another front - and ensured the continuation of the Ottoman war effort by opening up the way for material assistance from Germany.