A mixed salad dressed up in red, white and blue

In Making Americans: Immigration, Race, and the Origins of Diverse Democracy (2000), Desmond King offered an illuminating and trenchant analysis of the primacy of "whiteness" in successive official reformulations of American national identity. However, members of immigrant minority groups, he concluded, had embraced the metaphor of the salad bowl - rather than the melting pot - to articulate their belief in cultural pluralism.

The Liberty of Strangers extends and amplifies King's concern with the tensions between individualism and ethnic and racial group loyalties in the post-multicultural American polity. His main contention is that despite the "one people" rhetoric of American nationalism espoused by conservatives, group divisions have remained an integral and dynamic factor in the continuing evolution of American national identity. Where advocates of "assimilationist democracy" claim that group consciousness militates against patriotic feeling, the proponents of an "inclusive nationalism" argue that a community of groups strengthens rather than weakens a post-ethnic US. The homogenising melting pot never worked; the salad bowl continues to become more mixed in its ingredients while retaining a distinctively American flavour.

In a partial survey of 20th century American history, King reveals how group loyalties and divisions were imposed on or adapted by successive generations of voluntary (or involuntary) immigrants. But government policies promoting the acculturation of individuals into American society frequently had unintended or unforeseen consequences. "Americanisation" programmes applied to Native Americans and new European immigrants "often accentuated rather than diluted" their group consciousness. Also, proficiency in English did not automatically confer "American" credentials on East European Jews, West Indians, Puerto Ricans and Filipinos.

Ironically, whites also belonged to groups. After the Civil War, sectional reconciliation between the North and the South was achieved at the expense of former slaves, but the Confederate flag remained (and remains) a defiant symbol of a composite Southern white identity. Immigration exclusion laws directed against the Chinese and Japanese and the "national origins" quotas of the Johnson-Reed Act (1924) further "promoted a conception of American national identity as white".

Before the advent of the civil rights movement, African-Americans, subject to discrimination and proscription, attempted to make congregation out of segregation, while a minority were drawn to black separatist movements such as Marcus Garvey's Universal Negro Improvement Association. The maltreatment of African-Americans, the Second World War internment of Japanese-Americans, and racial classifications (still used in the US census) inadvertently served only to heighten group identity and resolve.

International events also affected American nationalist ideology. The First World War unleashed a tide of hysterical anti-German feeling across the US, with Germans and Irish the principal targets of programmes of "100 per cent Americanism". President Woodrow Wilson took the US into the war "to make the world safe for democracy", yet his Administration instituted racial segregation and discrimination in government offices.

The Second World War saw mass mobilisation against fascism abroad, yet African-Americans experienced discrimination and segregation in the armed forces and defence industries. Black protest was epitomised by A. Philip Randolph's March on Washington movement and the adoption by sections of the African-American press of the "double-V" campaign: victory over racism at home and the Axis powers abroad.

If King overestimates the extent of African-American protest in the war years, his assertion that the Second World War "both facilitated more tolerant views of ethnic identity in US society and forced changes to the segregationist political order" is close to the mark. Most important, "ethnicity was renegotiated to be a virtue instead of a defect".

After 1945, federal policies began to recognise "that American society is multiethnic and culturally diverse". But that recognition brought attendant problems, not all of them resolved: demands by African-Americans for monetary reparations for slavery and policies of affirmative action, bilingual educational programmes for groups whose first language is not English, and (although this is not discussed by King) the agendas of women and of gay and lesbian groups for equal rights.

As King observes, membership in the American polity is never static or secure. Post 9/11, Arab and Muslim Americans have discovered how suspect and precarious their citizenship is. Ironically, the War on Terror has fostered the promotion of both a "one nation under God" and a "salad bowl" portrayal of the US by the Bush Administration.

Group divisions, King concludes, "have historically proved fissiparous, have changed over time in response to new demands for political inclusion and unanticipated international pressures, but they have not dissipated".

American nationalism is not fixed but "continues to unfold in a non-teleological fashion, shaped by historically formed group divisions and government institutions".

The Liberty of Strangers is an incisive and significant contribution to the study of American identity. As important, it offers insights and perspectives on the problems and possibilities faced by all multiethnic democracies. It deserves an international readership.

John White is emeritus reader in American history, Hull University.