Italy, Napoleon once complained, is far too long. Even as the peninsula strove for unity in the 19th century, Goethe described it as "the shadow of a nation", and many Italians found themselves in surprising agreement. The late 19th-century statesman Giustino Fortunato declared that "the unification of Italy was a sin against history and geography", while one of his contemporaries warned that "the head and the tail will never touch each other, but if they are made to do so, the head will bite the tail".

Heading off in pursuit of Italy, David Gilmour finds instead a land and people defined enduringly by campanilismo (literally, the municipal bell tower) – a communal loyalty – and with little interest in nationalism except when "forced or cajoled". From the outset, Gilmour wonders if the Risorgimento, the national unification of Italy under Garibaldi, Camillo Cavour and King Victor Emmanuel II, was successful, or even necessary. As the country's current woes deepen, Gilmour longs for a land divided into small states, with regions such as Venice emulating relatively new European states like the Netherlands (although not, presumably, the former Yugoslavia).

It is a provocative and at times puzzling argument that takes Gilmour right back to the peninsula's prehistory and the myth of Hercules rescuing a bull calf. In a tour de force opening, Gilmour provides a wonderful survey of the region's limitations. Uniquely positioned to invite invasion, Italy has few rewards from its limited and unpredictable Mediterranean fishing industry. Its mountains (which "many Italians detest") and rivers have tended to impede rather than encourage trade and urban development. Even at its height, Florence was unable to subsist on local produce for more than five months a year. Gilmour is at pains to dismiss the bucolic myth of the land of Capri and chianti, gondolas and gorgonzola. The Italy we want to imagine bears little relation to reality.

Gilmour is incapable of writing a bad sentence and The Pursuit of Italy certainly offers a fluent and readable history. At every turn, the belief in a unified Italy is shown to be a mirage. When Cicero spoke of "the whole of Italy", his allegiance was really to Rome and his home in Arpinum. The great medieval communes had no concept of a nation, and are idealised somewhat by Gilmour as places where life was truly communal, with little "barrier between public and private lives". There is a sparkling account of the Venetian Republic and its tragic surrender first to Napoleon, then the "aberration" of its incorporation into greater Italy. But Gilmour expends most of his ire on the chaotic, disorganised period of intense realpolitik that led to the creation of the Kingdom of Italy in 1861 and which set the scene for the rise of fascism and the country's weak and corrupt postwar governments.

Gilmour insists that the Risorgimento was never inspired by a popular desire for national unity. Myth after myth is stripped away: Verdi was no real nationalist, his music carrying "a whiff of the fairground"; Cavour was indifferent to "what was happening in the peninsula beyond Piedmont"; King Victor Emmanuel believed the Italians were unfit for parliamentary government and understood only rule "by bayonets and bribery". Only Giuseppe Garibaldi escapes revisionism.

Nevertheless, behind Gilmour's argument lie some peculiar assumptions about nationalism. He argues that the Italian nation never existed before the 19th century, and even then it was imposed on its subjects for all the wrong reasons. But all modern nation states lay claim to their antique roots, and their popular support is always questionable. Is Italy really any different?

Gilmour has no time for Marxist explanations of the pitfalls of nationalism, but he somewhat oddly ends up endorsing a similarly old-fashioned celebration of the local and the parochial. Perhaps the book responds to a deeper disquiet with the limitations of the European nation state, at a time when multinational globalisation seems to be all the rage, but this is a long way from Gilmour's beloved campanilismo.

• This article was amended on 20 October 2011 to correct the name of the Italian king who reigned at the time of the unification of Italy to Victor Emmanuel II.