Military history of Italy during World War II

The participation of Italy in the Second World War was characterized by a complex framework of ideology, politics, and diplomacy, while its military actions were often heavily influenced by external factors. Italy joined the war as one of the Axis Powers in 1940 (as the French Third Republic surrendered) with a plan to concentrate Italian forces on a major offensive against the British Empire in Africa and the Middle East, known as the "parallel war", while expecting the collapse of British forces in the European theatre. The Italians bombed Mandatory Palestine, invaded Egypt and occupied British Somaliland with initial success. As the war carried on and German and Japanese actions in 1941 led to the entry of the Soviet Union and United States, respectively, into the war, the Italian plan of forcing Britain to agree to a negotiated peace settlement was foiled.

The Italian dictator Benito Mussolini was aware that Fascist Italy was not ready for a long conflict, as its resources were reduced by successful but costly pre-war conflicts: the pacification of Libya (which was undergoing Italian settlement), intervention in Spain (where a friendly fascist regime had been installed), and the invasions of Ethiopia and Albania. However, imperial ambitions of the Fascist regime, which aspired to restore the Roman Empire in the Mediterranean (the Mare Nostrum) resulted in Mussolini keeping Italy in the war, albeit as a country that was increasingly dependent upon German military support as in Greece and North Africa following the British counterattack.

With the Axis invasion of Yugoslavia and the Balkans, Italy annexed Ljubljana, Dalmatia and Montenegro. Puppet regimes were also established in Croatia and Greece, which were occupied by Italian forces. Following Vichy France's collapse and the Case Anton, Italy occupied the French territories of Corsica and Tunisia. Italian forces had also achieved victories against insurgents in Yugoslavia and in Montenegro, and Italo-German forces had occupied parts of British-held Egypt on their push to El-Alamein after their victory at Gazala.

However, Italy's conquests were always heavily contested, both by various insurgencies (most prominently the Greek resistance and Yugoslav partisans) and Allied military forces, which waged the Battle of the Mediterranean throughout and beyond Italy's participation. The country's imperial overstretch (opening multiple fronts in Africa, the Balkans, Eastern Europe, and the Mediterranean) ultimately resulted in its defeat in the war, as the Italian empire collapsed after decisive defeats in the Eastern European and North African campaigns. In July 1943, following the Allied invasion of Sicily, Mussolini was arrested by order of King Victor Emmanuel III. Under Mussolini's successor Pietro Badoglio, Italy signed the Armistice of Cassibile with the Allies on 3 September 1943. This was announced on 8 September 1943, with Germany invading and occupying much of Italy and its previously occupied and annexed territories. Mussolini would be rescued from captivity a week later by German forces.

On 13 October 1943, the Kingdom of Italy officially became a co-belligerent of the Allies and formally declared war on its former Axis partner Germany. The northern half of the country was occupied by the Germans with the cooperation of Italian fascists, who formed a collaborationist puppet state (soldiers, police, and militia recruited for the Axis); the south was still controlled by monarchist forces, which fought for the Allied cause as the Italian Co-Belligerent Army and Italian resistance movement partisans (many of them former Royal Italian Army soldiers) of disparate political ideologies operated all over Italy. Unlike Germany and Japan, no war crimes tribunals were held for Italian military and political leaders, though the Italian resistance summarily executed some political members at the end of the war, including Mussolini on 28 April 1945.