I'm interested in both pre-war monarchy Yugoslavia and post war socialist Yugoslavia's relationship with the USSR, and later members of the Warsaw pact. My understanding of events are that they were socialist but distinctly more moderate than the Warsaw pact countries but please correct me if this was not the case. I was wondering how well they got on with the more extreme communist, Stalinist ect countries with people like Stalin's desire to clamp down on variations from Stalinist communism mixing with his thirst for expansion.
Yugoslavia, for most of the Cold War, is best described as a neutral, unaligned power^1. It had good relations with some Warsaw Pact countries (like Albania^2) but was never a full member of the alliance^1, or a part of the USSR's sphere.
To understand why, we need to go back to the Second World War itself. So in early April of 1941, the Axis decided to shore up their southern flank in preperation for the main event of the invasion of the Soviet Union. To do this they invaded the pro-Allies Kingdom of Yugoslavia, and pro-British Kingdom of Greece. The invasion of Greece was part of Mussolini's plan to recreate a Roman Empire, but the invasion of Yugoslavia (while increasing Italy's territorial ambition) was the product of the anti-Axis coup in March of 1941. It replaced the increasingly pro-Axis regency with Peter II; a 17 year old king. This prompted Germany to ensure a regime change occurred by invading, giving some land to Italy, and creating the Croatian puppet-state.
Skip ahead to late-1944 and 1945 where the partisans who have been fighting the Axis occupiers throughout the war finally start to gain momentum. With Western Allied airstrikes, and the pressure put on German forces by an ever encroaching Red Army; the Yugoslav partisans under Josip Broz Tito were able to recapture Belgrade and formally mark themselves as the only country during the Second World War to liberate themselves. As such, the Red Army had little power in the country unlike in Eastern Europe where it occupied large parts if not the entirety of most of the countries in the region.
Tito's success as leader of the partisan forces allowed him to take control of the country^2 in the post-war years and secure dominance in the Yugoslavian Communist Party. However, Stalin's refusal^4 to get involved in the Greek Civil War, the Soviet lack of any nuclear weapons, and Tito's refusal to see Moscow as the metropol of Communism led to a split between the two leaders. This was further solidified when Yugoslavia stabilised relations with neighboring Western countries. The split was reinforced by the Soviets with their exclusion of Yugoslavia from the Warsaw Pact.
While many other Eastern European countries attempted a split from the USSR (most notably the 1953 German Worker's Strike, the 1956 Hungarian Revolution, and the 1968 Prague Spring) none had the internal power and history of conflict against Soviet influence as the Yugoslavs.
To this end, the Iron Curtain never included Yugoslavia which even went as far as to be a founding member of the Non-Aligned Movement^1 with India, Egypt, Indonesia, and Ghana.
Sources:
J.W Young, J Kent, International Relations Since 1945 (Oxford, Oxford University Press, 2013)
A Applebaum, Iron Curtain: The Crushing of Eastern Europe (London, Penguin, 2013)
L Holmes, Communism: A Very Short Introduction (Oxford, Oxford University Press, 2009)
S.S Montefiore, Stalin: Court of the Red Tsar (London, Orion Books Ltd, 2004)