Remember ANY of the big five can keep anyone out of the UN, the US did that for decades in regards to Red China. Red China was only admitted once US opposition to replacing Taiwan with red China ended did Red China get a seat.
Secondary, the UN will NOT seat a country if they is any opposition to seating that country, for Example, when Germany was divided, neither West Germany nor East Germany had a seat (Both did get a seat in the 1970s when both agreed NOT to oppose each other's admittance, but note it was by agreement of BOTH Countries AND their respective allies, the US and the USSR). North and South Korea did NOT join the UN till 1991 for both oppose each other admittance (The fall of the Former Soviet Union forced North Korea to look more "peaceful" so agreed to a solution similar to Germany's solution of 1973). On a similar scale when the former Yugoslav Republic of Macedonia wanted into the UN, Greece opposed it UNTIL it took the "Provisional Name" of the "Former Yugoslavia Republic of Macedonia". This had more to do with internal Greek Politics (and the breakup of the old Ottoman Empire in the late 1800s, then anything else).
Korea's admittance into the UN:
http://findarticles.com/p/articles/mi_m1309/is_n4_v28/ai_11715979http://www.state.gov/r/pa/ei/bgn/2792.htmhttp://books.google.com/books?id=dB_8L4ysZrEC&pg=PA71&lpg=PA71&dq=Korea+UN+membership&source=web&ots=UgHFCsOfwv&sig=Nq7EZhf7Z9r0GeAWRyj_A7wItJo&hl=en&sa=X&oi=book_result&resnum=5&ct=result#PPA70,M1Articles on Taiwan and why it should be (And is NOT) a member of the UN:
http://www.davekopel.org/Misc/OpEds/Taiwans-right-to-UN-membership.htmMore on Macedonia:
http://en.wikipedia.org/wiki/Macedonia_naming_disputeAs to the Vatican the following Countries recognize it as an independent country:
http://en.wikipedia.org/wiki/Diplomatic_missions_of_the_Holy_SeeMy point was simple, many countries, including the US, recognize the Vatican as a sovereign nation. UN membership is affected by politics, especially among the five permanent security council members. Right now Red China and the Vatican have had a dispute over the Catholic Church in China. China says the Catholic Church in China is independent of the Vatican, the Vatican says it is NOT, and the only reason Chinese Bishops maintain their independence is do to political pressure from the Red Chinese Government. This is consistent with Red Chinese demand for control over all POTENTIAL political opposition. The Red Chinese remember the Boxer rebellion of the early 1900s, the 1860s Civil War, and the raise of their own Communist Party, all of which rose out of existing Religious/Reform groups that later spawned political opposition. Thus the Red Chinese do NOT want ANY independent Reform/Political groups on anything but the local level (And even then watched carefully). This includes the Catholic Church but much more (Including the Dalai Lama of Tibet and his followers, any any other group that "might" give raise to opposition to the party).
Now, this opposition to ANY outside political organization, the Vatican is just the largest one NOT a member of the UN THAT has potential membership inside China I.e. the Catholic Bishops and Priests). Arguments over who can name Bishops in China is constant between the Vatican and China. The Chinese Government does NOT want any independent organization in China, let alone one with connections with an outside power base (i.e. the Vatican).
Given the above, the Red Chinese Government has consistently opposed ANY admittance of the Vatican into the UN. Italy has not such problems, neither does the rest of the world (with the possible exception of Russia) but since Red China is on the Security Council, it can veto any one nations efforts to join the UN (Through once in, no nation has ever been kicked out or left, unlike the old League of Nations which had several member leave in the 1930s, even as it refused to admit the Soviet Union). For at least the last 30 years the dispute between the Vatican and Red China as to the Catholic Church in China has been a point of contention between the two, and the reason China will always threaten a veto over any effort to admit the Vatican. Until China's opposition is ended, probably do to some deal like the one involving East and West Germany in 1973 OR a change in the World Wide Political situation like the fall of the Soviet Union in 1991, I see no change.
Now Russia does NOT have diplomats with the Vatican, but does permit the Vatican to have a minster in Russia. This has to do with the Raise of the Orthodox Church in Russia under both Yeltsin and Putin. The Orthodox church is no where near the power it had under the Czars, but it is an important institution inside Russia. The dispute between the Patriarch of Moscow and the Vatican over Catholics inside Russia has been a sticking point between the Patriarch and the Pope. Technically all Christians (That is Catholics AND Orthodox) in a country must be under the Bishops of that country. The Catholic Church in the US has long have a history of duplicate Bishops in North American (Generally Latin rite dominates, but Greek-Catholics rites, technically under Rome, tend to have independent diocese over the same territories as Latin Rite Diocese). The Patriarch views this as wrong and objects to the Pope naming bishops for Latin rite churches in Russia, The Patriarch believes he should have that right. This has been a point of dispute ever since Stalin merged the Uniate Orthodox Church (who recognize the Pope as the head of the Church) with the Orthodox Church of Moscow in the late 1940s.
A complicating factor is, even today, a main source of funds to Orthodox Churches in the former Soviet Union and Warsaw Pact Nations, have been money from member Churches located in the US. Technically they should be under the local Latin Rite Bishops, but do to long custom, are under their own Bishops.
Now the Russia situation is NOT as critical as the Chinese situation, but it is a factor and why another member of the Security Council does NOT want the Vatican in the UN. I do NOT think it is a serious factor for the Chinese seem to have a much greater demand that the Vatican NOT be seated, but the Situation with Russia and the Russian Church has been and continues to be a point of conflict between Russia and the Vatican.
List of Uniate Churches:
http://orthodoxwiki.org/UniateMy point is the Vatican meets ALL of the requirements to be a member of the UN EXCEPT the most important one, agreement by all FIVE Permanent members of the Security Council. Why even push it to far if at least one says they will veto such an admission? Thus why the push has failed over the years and will continue.
As to WWII and Pope Pius, he was a diplomat and the first rule of any diplomat is NEVER offend, thus Pius XII was never going to offend anyone, be it Hitler or Stalin. Pius was one of the first people in Europe to say you can NOT trust Hitler (More to do with Hitler's failure to follow the Concordat he signed with the Vatican then anything else, but that came to a head in 1938 under Pius XI who preceded Pius XII, but Pius XII was part of the Vatican that opposed Hitler's ignoring the Concordat).
AS to Hitler, most people in Government at that time are NOT innocent. Whey did Hitler's aide fly to Britain in the Spring of 1941? Was that part of a proposed agreement to end the war with Britain in exchange for Britain giving Hitler a free hand against Russia? Some of the records of that flight and exchange is still secret even in Britain. I can see Churchill entering into negotiations with Hitler in late 1940 early 1941, for no actually fighting was occurring at that time (France was under Hitler's Rule, the Battle of Britain was over, the Balkans were not yet invaded by Hitler, Africa was an Italian Debacle, soon to be undone by Rommel but that was in the Future), the Bismark was sunk but overall no real conflict between Germany and Britain (Yes they were at War, Bombing each other's cities, but again to no real effect). I could see Churchill trying to work out a compromise to end the war, get German Forces out of France, even if that meant Russia under Hitler (Poland was lost, the best Britain could hope for in late 1940 early 1941 was France). I could see such a deal being discussed, after WWII Churchill sat down with Stalin and negotiations with Stalin in the same regards to the Countries of Eastern Europe). I also suspect FDR veto it, telling Churchill if he signed a peace or truce with Hitler, FDR would cut off lead-lease to Britain.
My point is whatever crimes Pius XII did (and there is debate to what if any crimes he did commit) they are people who did greater crimes at the same time) crimes by Nations have NOT kept them out of the UN (The Former Soviet Union for Example and later Cambodia under Pol Pot, who retained its UN Seat for years after losing power in Cambodia do to the Invasion by Vietnam, do to the support of Red China). The issue for the UN should be "will the addition bring about increase discussions that will avoid future conflicts?" If the answer is yes, Membership should be granted, if not then no. I will NOT say one way or anther as to the Vatican, but UN membership does NOT mean a Nation is NOT Sovereign, all it means is that sometime in the past it had approval of the UN as a whole AND all five permanent members of the Security Council.