Issues of cultural and regional diversity in large developed states have become major themes in contemporary political debate.
How can cultural diversity and political solidarity be reconciled in Britain? Is multiculturalism compatible with French republicanism? Does the dramatic growth of the Hispanic community in the United States undermine its national unity? How will tomorrow's national elections in Spain affect its efforts to reconcile national unity and regional diversity after this week's bombing tragedies in Madrid?
David Goodhart, editor of Prospect magazine, has provoked a lively debate in Britain about the relationship between cultural diversity and the political solidarity needed to underpin its welfare state. He argues that too much diversity affects the trade-off with welfare in a "progressive dilemma". He quotes research arguing the US does not have a European-style welfare state because too many people at the bottom of the pile there are black or Hispanic.
Goodhart argues that since the thickest solidarities are often found among ethnic minority groups, "we are more tolerant than, say, France because we don't care enough about each other to resent the arrival of the other". In Blairite fashion he seeks a "melting pot" third way based on citizenship education between the nationalist right's coercive assimilation and a multiculturalism which rejects a common culture.
There has been a strong response to Goodhart's essay, both in the Guardian, which republished it, and on the Prospect website (www.prospect-magazine.co.uk/replies.asp). Well-known writers on these subjects such as Will Kymlicka, Bernard Crick, Amitai Etzioni, Nathan Glazer, Nigel Harris, Bhikhu Parekh and Saskia Sassen show he has touched a real nerve.
He pays too much attention, they say, to the US model, compared with Canada and Sweden which combine high levels of immigration, multiculturalism and welfare redistribution; he ignores national diversity in the UK by adopting a very English perspective; Britons share a common state, not a common culture, which was never as spontaneously homogenous as he describes, since class and region divide them; and history shows the UK like other large states has managed to turn immigrants into a solidaristic "we" in no more than a couple of generations of political struggle and creative cultural adjustment.
In France, for example, as Saskia Sassen points out, one third of the population is of second or third generation foreign ancestry. The French approach to cultural diversity is much more assimilationist than Britain's. It is based on the integration of individuals into republican citizenship, not on collective integration or recognition of communities.
Diversity has been highlighted by the new law banning the Islamic veil in schools. But the existence of separate disadvantaged Muslim communities in major French urban centres is a standing failure of assimilation to which the French are only now becoming intellectually and politically adjusted. There are belated efforts to encourage socio-economic integration.
The French mindset resists multiculturalism, while communitarianism has become a swear word. Political theorists such as Dominique Schnapper are struggling to define a "tolerant republicanism" for a more diverse France.
Ironically this means learning the lessons from French Quebec, the source of much creative thinking on multiculturalism; and from France's own changing role in a more diverse and Anglophone Europe where it can no longer be assumed to carry universal weight and must fight to protect its own cultural specificity.
The US political scientist Samuel Huntingdon became controversial 10 years ago with a famous article predicting a clash of civilisations would replace the Cold War geopolitical conflict between the US and Soviet blocs. It was widely criticised for cultural determinism. His latest work is likely to be equally contested.
In the current issue of Foreign Policy magazine, he argues that the persistent flow of Hispanic immigrants threatens to divide the US into two peoples, two cultures and two languages. This would definitively break a national culture in which immigrants assimilated to Anglo-Protestant values of thrift, social mobility and political liberty. He quotes Theodore Roosevelt with approval: "We must have but one flag. We must have but one language." There can be no Americano dream but only an American one - in English.
Huntingdon sounds like one of Goodhart's coercive assimilationists. But he admits that even the nationalist right around George Bush has accepted the reality of Hispanic cultural power and political influence.
In Spain, Jose Maria Aznar certainly comes from the nationalist right. He sounds like a classical Castilian coercive assimilationist to Basques, Catalans and other regional peoples there. The bombings have radically dramatised Spanish unity and diversity. But its controversies are based on territorial not immigrant politics.
Such centre-periphery diversities are fruitfully compared in Spain, the UK and France in a new book edited by Joseph Ruane, Jennifer Todd and Anne Mandeville, Europe's Old States in the New World Order (UCD Press). It finds Spain's nations and regions are adjusting well but distinctively to these pressures, as are French and British ones. Spain's diversity is solidly entrenched constitutionally and politically, however challenged it is by the unresolved Basque question.