The Balkans Campaign was an operation carried out by Nazi Germany and Italy against two countries in the Balkans, Greece and Yugoslavia. In October 1940, the Italians attempted to invade Greece in what became known as the Italo-Greco War. However, it went badly, with the Italians being pushed back into southern Albania. In April 1941, Hitler decided to help his ally by attacking Greece from Bulgaria. After initial success, Germany set up the Hellenic State, a puppet regime, in northern Greece. The Prince of Yugoslavia, Paul I, wanted to join the Axis, but Serbian officers within the Royal Army did not. They committed a coup d'état, putting his relative into power, Peter II, who decided to join the Allies.
After World War I, the Italians began attempting to bring Albania into their sphere of influence. The attempts rose after 1925, by will of Benito Mussolini, the fascist dictator of Italy. It was part of his plan to create a "New Roman Empire". In 1928, however, Albania became a kingdom under Zog I, the former Prime Minister of Albania. In April 1939, Mussolini's forces entered Albania and occupied the country, overthrowing Zog I.
It only heightened Mussolini's ambitions, and he wished to include other countries on the Mediterranean, including Greece. He had occupied islands and territories on the mainland that were dominantly Greek, and refused to return them to the Greek government, despite previous agreements. On 23 September 1928, the leader of Greece declared friendship between the two countries. However, Ioannis Metaxas came to power soon afterwards and began reorganizing the Greek Army. It was retrained and given modern weaponry and equipment, greatly raising it's state. It also made a line at the Greek-Albanian border known as the Metaxas Line, and created many supply warehouses around the country.