As for the states and their reasons for joining the second world war - a lot of bloodshed could have been avoided if they actually joined in on time. Fashionably late is not really something that should occur during a war.
On time? You mean 1935 when the Treaty of Versailles was first violated? That would have been a little difficult, don't you think, as the US refused to ratify that treaty? Nobody bothered to be 'on time.'
An interesting fact about World War One relating to media censorship engendered dissemination of false opinions and even entire misguided political movements including the early popularity of Nazism was revealed by the great journalist George Seldes:
'At end of the war, he obtained an exclusive interview with Paul von Hindenburg, the supreme commander of the German Army, in which Hindenburg acknowledged the role America had played in defeating Germany. "The American infantry," said Hindenburg, "won the World War in battle in the Argonne." Seldes and the others were accused of breaking the Armistice and were court martialed. They were also forbidden to write anything about the interview and it never appeared in American news media. Seldes believed that blocking the interview proved tragic. Unaware of Hindenburg's direct testimony of Germany's military defeat, Germans adopted the Dolchstoss or "stab-in-the-back" theory that Germany only lost because it was betrayed at home by "the socialists, the Communists and the Jews," which served as Nazism's explanation for Germany's defeat. "If the Hindenburg interview had been passed by Pershing's censors at the time, it would have been headlined in every country civilized enough to have newspapers and undoubtedly would have made an impression on millions of people and became an important page in history," wrote Seldes. "I believe it would have destroyed the main planks on which Hitler rose to power, it would have prevented World War II, the greatest and worst war in all history, and it would have changed the future of all mankind."'
http://en.wikipedia.org/wiki/George_Seldes