*Sigh*
Ok, I'll cave and spill the rest of the beans. here goes:
1. When created in 1918, what was the country's official name?
As several got correct, it was "The Kingdom of Serbs, Croates and Slovenes".
2. How many languages were natively spoken in the country?
It's almost impossible to answer this one wrong.

Serbo-Croat, Slovenian, Macedonian, Albanian, Hungarian, German, Romanian, Italian, Bulgarian, Greek, Turkish, Armenian, and a plethora more left over from the migrations of the Ottoman-Habsburg wars.
3. It was supposed to be a marriage of equals, but the circumstances of its creation made that impossible in 1918. Why?
As again some got correct, Serbia already existed as a state and had all the trappings of a state; a government, a bureaucracy, an army, a tax system, etc. In 1918, instead of several equals coming together to form a union, the other republics were effectively absorbed by Serbia. The Serbian dynasty (Karadordevic) became the kingdom's rulers, the Serbian Army simply started taking recruits from the other regions, Serbian bureaucracy was set up in the other regions, etc. Does this sound like a recipe for success to you?
4. France attempted to create an anti-German alliance in Central & Eastern Europe in the 1920s with Poland, Czechoslovakia, Romania and Yugoslavia but in the end only the last 3 joined. The alliance - L'Entente petit - failed because the 3 eastern members concentrated their efforts against another country instead of Germany; who?
As at least one person got right, this other state was Hungary. Why? All three
Entente states (Romania, Czechoslovakia, Yugoslavia) had taken large amounts of Hungarian territory - much of it with non-Hungarian ethnic groups but still including some 3 million Hungarians - and they were all determined to keep Hungary from taking it all back. They were right to be afraid; Hungary did want it back, and spent much of the 1920s and 30s agitating to that purpose. Sadly, these border disputes kept the region divided and open to outside manipulation, which is precisely what Hitler and Mussolini did.
5. What state was Yugoslavia's mortal enemy in the 1918-1939 years? (Hint: Think real estate!)
Several got this one right; Italy. Mussolini wanted the whole eastern Mediterranean shore.
6. In 1929 a Croatian deputy in the national assembly was assassinated in full view of the parliament. What two major changes did this precipitate?
One person got this right; first, the Yugoslav king Alexander declared a royal dictatorship, and secondly he changed the country's name to the familiar "Yugoslavia".
7. Who was IMRO and what did they do in 1934 regarding Yugoslavia?
I believe two people got this one; The
International
Macedonian
Revolutionary
Organization was a terrorist organization devoted to attaching most of Macedonia to Bulgaria. It was founded in 1893 and had a powerful deathgrip on the Bulgarian government for decades until finally being gutted and almost destroyed by King Boris in the 1930s. Its most infamous act was the assassination of the Yugoslav King Alexander in Marsailles in 1934. King Boris had been trying to improve relations with the Greeks and Yugoslavs, and IMRO needed to eliminate King Alexander as a reformist threat to their agenda; he did away with many of the Yugoslav repressions in Macedonia and therefore wasn't a good scapegoat anymore. They still exist today, BTW;
here is their website. (In Macedonian & Bulgarian their initials are "VMRO", or in the Cyrillic alphabet "BMPO".)
8. In 1941 the Yugoslav government was moving towards signing an agreement with Hitler that allowed German use of Yugoslav railways and roads and gave almost exclusive rights of purchase of Yugoslav produce to Germany, and yet a month later Germany was invading Yugoslavia. What went wrong?
Two folks got this one, I believe; Prince Pavel (Paul) sent his prime minister Cvetkovic to Vienna on 25. March, 1941, to sign a treaty of amity with Hitler but two days later a coup removed both the Prince and his government. The succeeding government led by Dusan Simovic was strongly pro-British, and the coup was immensely popular throughout Serbia. (Croatia took the coup as an excuse to bolt.) Hitler began his invasion on 6. April...
9. The Hungarian Prime Minister, Pál (Paul) Teleki, was heavily pressured by Hitler to join the German invasion of Yugoslavia in 1941. (Yugoslavia had inherited significant numbers of ethnic Hungarian areas after World War I.) Teleki finally agreed, but the night he gave the order for the Hungarian Army to cross the Drava River into Yugoslavia, Teleki took his pistol and blew his brains out. Why?
Ah, good ol' Teleki Pál. Interbellum Hungary was firmly controlled by the old aristocracy, though they functioned through a modern form of government. Teleki had resolved most outstanding issues with Yugoslavia (as the neighbor who had taken the least of Hungarian territory in 1920) and signed a treaty of friendship and peace with Belgrade so he could concentrate on Romania and Czechoslovakia. Two weeks later Hitler heavily pressured him to parttake in the German invasion of Yugoslavia... Teleki's aristocratic sense of honor was compromised and while he finally caved in and gave the order for the Hungarian Army's participation in the invasion, he immediately went back to his office and killed himself. He may have been driven to this act as well by a meeting with the British Ambassador, a personal friend, who declared this a treacherous act of infamy that would be remembered after the war. Teleki knew he would go into the history books as someone who betrayed his word...
10. What are Chetniks?
Several got this right. The
Chetniki were mostly Serbian peasant-soldier partisans who wanted to re-instate the monarchy after the war. They are loosely related to a similar peasant-soldier in the region from Habsburg days, the
hajduks.
11. Who was Dradza Mihailovic, and why did he end up being hung in 1946?
One person got this question completely correct; Mihailovic was the leader of the Chetniks and while he often attempted to cooperate with other partisan groups (like Tito's comunists) they fought vociferously against him so Mihailovic often sought accommodation with the Germans in his battles with Tito's partisans. This branded him as a collaborator, and he hung for it after the war.
12. Who was Josip Broz, and how is he remembered today?
Yes, Tito. Someone got this right too. Broz was a half-Slovene, half-Croat who had a long career as a revolutionary and in his many travels had managed to accumulate a alarge number of pseudonyms. Tito was just one of them, if the most famous.
13. What percentage of Yugoslavia's popualtion died in the war:
A. 3% C. 10%
B. 30% D. .05%
C. 10%.
14. What did Tito do over Istria in 1946 that infuriated both Washington and Moscow?
No one got this right; the key word was "over". Tito's partisans had occupied large parts of Italian Istria after the war, and even parts of southern Austria. The U.S. and British armies had to drive them out of these territories (including elaborate negotiations over Trieste), so in retaliation Tito ordered an American transport shot down when it was flying over Istria in 1946. It doesn't need to be explained why Washington was furious about this, but Stalin was also not amused because this act of aggression occurred without his knowledge or consent. Stalin didn't need one of his little puppet dictators in Eastern Europe starting World War III on him....
15. Tito attempted in 1945-47 to first incorporate Albania into Yugoslavia, then create a confederation with Bulgaria, and finally send material aid to the Greek communist rebels. However, he was thwarted in all these schemes. By whom?
Stalin again, as someone got correct. For reasons related to Question # 15, Stalin did not want his puppets taking any initiatives without his approval.
16. The world's communist leaders were congregating in Bucuresti/Bucharest in 1948 for a conference, but Tito was not invited. Why?
As someone got right, this is the critical break between Belgrade and Moscow. In early 1948 Stalin shut off economic aid to Yugoslavia, by March he withdrew all Soviet advisors, and in June 1948 the Yugoslavs were expelled from the Cominform.
17. Milovan Djilas was a native Montenegrin and a lifelong communist who fought beside Tito in the war and by 1955 was the 4th most powerful man in Yugoslavia. He was soon sitting in a prison cell though, why?
I'm surprised no one got this one. Or maybe, I'm just a little too old.... Djilas had been a true believer in communism until he saw it in practice for years throughout the Soviet Union, China and Eastern Europe, and he published his fateful work "
Novy klas" ("The New Class") about how a new and corrupt ruling elite had sprung up in the communist countries. Djilas said this new class was even more corrupt than its capitalist predecessors, and much more oppressive. You can maybe understand now why Djilas did some jail time...? he since wrote many books on the subject, including one on his various personal meetings with Stalin. If you haven't read "The New Class" and you're interested in 20th century history, shame on you!
18. After Tito died in 1980, who became President?
Trick question. Tito was succeeded by a rotating presidency council. No one person took over. This is one of the reasons Yugoslavia declined so rapidly in the 1980s, because you can't have a dictatorship without a dictator or with a council of dictators...
19. In the mid-1980s an old apparatchik of the system paid a visit to Kosovo where he became concerned about the rising tide of Albanian nationalism. He made a dramatic street speech proclaiming eternal Serbian sovereignty in Kosovo. Who was this?
As almost everyone got right, this individual and budding nationalist fanatic was Slobodan Milosevic.
20. What was the first republic to break away from Yugoslavia, after a 3-day war in 1991?
I think at least one got this right: Slovenia.
21. Last week's compromise between Serbia and Montenegro was a last-ditch desperate attempt by Belgrade to keep the Montenegrins from bolting. Aside from pride and nationalism, why was Belgrade so concerned about losing Montenegro? (Hint: it goes back to a problem that Serbia had in the First Balkan War of 1912-13, which resulted in the Western Powers creating Albania to thwart the Serbs...)
Two got this one correct. The issue was sea-access. Serbia without Montenegro is land-locked, as it was before World War I. The Great Powers of 1913 had created Albania specifically to block Serbia - a Russian ally - from the Adriatic Sea.
Bonus question: What does "Yugoslavia" mean?
And as a few got right, "Yugoslavia" means "South Slavia". The Serbs, Croats, Slovenes and macedonians all belong to the Southern branch of the Slavic family of languages.
Great work folks! Thanks to all who participated!