 Complete the following phrase:  In 1941, during the Helleno-Italian War, when Hitler demanded passage around the Kingdom of Yugoslavia to attack Greece, the Regent Prince Pavle of Yugoslavia attempted to appease Hitler by offering a non-aggression pact but, ultimately, signed the Tripartite Pact that would allow German passage. In return, the Greek city of Thessaloniki was promised to Yugoslavia. Two days later the army, aided secretly by the UK and the USSR, 