One thing I do hear a lot about WW2 is how it created, for lack of a better phrase "war solidarity" amongst the populace - people were more united and internal conflicts less common. The Nazis promotion of the volksgemeinschaft concept could be seen as a form of this (and I have heard that the promotion of the volksgemeinschaft concept was why there wasn't the mass rebellion you saw in Germany at the end of WW1. I hear about how people were more self-sacrificing and friendlier and the like. There was a book published which, if I remember correctly, argued that WW2 helped ease out social differences between white Americans (the various ethnic groups), who had previously distrusted each other a lot (between WASPs and Southern European Catholics, for example), as well as helping pave the way for the Civil Rights movement.
However I also have heard claims that solidarity wasn't really that common - different social classes still hated each other and class conflict never abated, different ethnic/racial/religious groups still massively despised each other and that the idea of wartime solidarity and national unity was really more propaganda that, while it may have had a grain of truth, was largely fabricated - most people did not feel any sense of social solidarity.
Now this latter claim is rather jarring since it contradicts a lot of what I hear about the war but at the same time I also know that propaganda of the era tried to avoid encouraging divisions at home and so may have downplayed any. So I guess my question is "to what extent did WW2 actually create any sense of social solidarity in the participant countries (and what differences were there between nations)?"
So to some extent war certainly helped create some sense of solidarity between individuals. The concept of the ‘band of brothers’ and the camaraderie which developed through military service could help to bring disparate social groups together. Likewise with wider society as a whole, the war offered people a common enemy and a common goal, which could likewise help to create solidarity by promoting a stronger vision of the collective self against the enemy other.
However, generally these forces for solidarity would not prove strong enough to dismantle social antagonisms, which would often return after the end of the war.
Jonathan Fennel has recently published a new book, ‘Fighting the People’s War’ which is about the British and Commonwealth Armies during the Second World War. Fennel discusses and describes the connection between war experience within the British Empire, and post-war social changes, such as decolonisation, and the establishment of welfare states. Fennel argues that through fighting, Imperial subjects came to demand something for their sacrifice, broadly, a more inclusive and progressive society. While not necessarily solidarity itself, this would seem to suggest a similar theme to that mentioned in your question.
The war could also increase solidarity across national borders. During the war the BBC launched the V for Victory campaign, which used the slogan “Europe against the Germans”, in a display of European solidarity. The campaign itself was even created by a Belgian refugee living in Britain, Victor de Laveleye. The historian Wendy Webster in her article, ‘The British Resistance Narrative’ argued that during the war Britain saw itself as closer to Europe than at any other point in the twentieth century. This is interestingly contrasted with the post-war identity construction of the British who later promoted a narrative which self-isolated Britain from Europe as a lone power. Such examples (and anti- examples) of transnational solidarity are also evident in the development of the post-war international communities which led to the likes of the European Union.
The question is rather complicated though to answer in entirely. Firstly, it should be noted that simply promoting solidarity and community spirit is not enough to stave off rebellion - Volksgemeinschaft after all was first conceived during the First World War.
Secondly it varied by region. Some, like the Commonwealth nations I mentioned previously could arguably have experienced greater communal solidarity, but in others the war exacerbated social divides. For example in areas of Eastern Europe, as a reaction to the Völkisch policies and aggression of the Third Reich, there was a considerable amount of hostility and violence carried out against the non-autochthonous German communities in states such as Czechoslovakia and Poland. And conversely, while for some groups solidarity improved, this was not necessarily a positive thing. For some nationalist groups in the formerly occupied territories, the war has in years since been mythologised as a prosperous period, with the racial cleansing of some groups perceived as outsiders, such as the Jewish, Roma and Sinte communities contributing to the perceived health and solidarity of their respective national groups. Further, in many communities there were, and often still are, wounds which have failed to entirely heal since 1945, particularly in relation to collaboration. In Poland for example, large numbers of individuals, often Polish citizens considered ethnic Volksdeutsche, were forcibly conscripted into the Wehrmacht, and to this day the association of a ‘grandfather in the Wehrmacht’ is negatively viewed and highly stigmatised. During the 2005 Polish presidential election, this was the case for politician Donald Tusk, whose grandfather was allegedly one such individuals, in a controversial case known as the ‘Afera wehrmachtowa’.
This is really a rather large question, and I’m afraid that without going into very great amounts of detail no definitive answer can be given. While some communities may have gained solidarity, others became more fractious. However, the particular characterisation of which description fits a particular area best is also one influenced by perspective. To an ethnically German Pole, society may seem more divided in the post-war period, while for an ethnically Polish individual the opposite may appear true.
Hopefully this somewhat generic overview has helped answer your question, and with luck some other posters can jump in with more specific examples.