World War II/German and Italian Attack in the Balkans
The Axis attack began on the 28th of October 1940, when Italian troops attacked and overran the Greek Border Guards outposts in Hepirus and west Macedonia. This occurred after the Italian Ambassador to Greece, Gracci, essentially blackmailed the Greek Prime Minister Ioannis Metaxas by requesting his permission on the deploying of Italian troops into Greece's territory.
Initially, the Italian Army made big gains, but Greek troops forestalled their offensive and even launched a counter-offensive on November 1940, overthrowing the Italians and capturing several ground into the Italian-occupied Albania. The situation worsened with the arrival of British troops on February 1941, so the Germans were forced to join the Italian attack on Yugoslavia and Greece, causing the collapse of both countries.