Final answer:
Italy entered World War II following the defeat of France by Germany in June 1940. The Italian invasion occurred alongside the establishment of the Axis Powers' control over Europe, but it was their military vulnerabilities that exposed the Axis' overextension. The eventual Allied invasion of Italy marked a turning point in the war.
Step-by-step explanation:
Italy formally entered World War II after Germany defeated France. This event occurred in June 1940 when German troops marched into Paris, and shortly thereafter Italian troops invaded Southern France. The defeat of France was a significant milestone in the war, leading to the establishment of German-controlled Northern France and Vichy France, a puppet state in the south. Meanwhile, the Axis Powers, comprising Italy, Germany, and Japan, had been established earlier following the Spanish Civil War and the economic sanctions on Italy after its invasion of Abyssinia. The strong bond between Italy and Germany, reinforced by the treaty of friendship and the concept of a 'Rome-Berlin axis', was meant to solidify their position in Europe against the Allied forces.
The events preceding Italy's entry into the war included significant developments such as the conquest of several European countries by Germany, and the Axis Powers' control over much of Europe and North Africa. However, the German invasion of the Soviet Union, which happened after Italy's declaration of war, marked a turning point and highlighted the overextension of Axis forces. Italy's invasion of Greece also showed the need for German reinforcements in the Balkans, demonstrating Italy's military vulnerabilities.
Allied forces eventually began the invasion of Southern Europe, aiming to drive Italy out of the war and push back against German troops. The eventual defeat of Italy in Sicily and the Allied invasion symbolized the beginning of the end for the Axis presence in the region, with Italy surrendering in 1943.