The Greco–Italian War, also called the Italo–Greek War, Italian Campaign in Greece, and the War of '40 in Greece, took place between the kingdoms of Italy and Greece from 28 October 1940 to 23 April 1941. This local war began the Balkans campaign of World War II between the Axis powers and the Allies and eventually turned into the Battle of Greece with British and German involvement. On 10 June 1940, Italy declared war on France and the United Kingdom. By September 1940, the Italians had invaded France, British Somaliland and Egypt. This was followed by a hostile press campaign in Italy against Greece, accused of being a British ally. A number of provocations culminated in the sinking of the Greek light cruiser Elli by the Italians on 15 August. On 28 October, Mussolini issued an ultimatum to Greece demanding the cession of Greek territory, which the Prime Minister of Greece, Ioannis Metaxas, rejected.

The Balkans campaign of World War II began with the Italian invasion of Greece on 28 October 1940. In the early months of 1941, Italy's offensive had stalled and a Greek counter-offensive pushed into Albania. Germany sought to aid Italy by deploying troops to Romania and Bulgaria and attacking Greece from the east. Meanwhile, the British landed troops and aircraft to shore up Greek defences. A coup d'état in Yugoslavia on 27 March caused Adolf Hitler to order the conquest of that country.