The conservative education minister, Esperanza Aguirre, wants every Spanish child to learn a curriculum that emphasises the "unitary character of Spain's past". The proposal, launched in the form of a decree, has whipped up a storm of outrage among the proudly independent Basques and Catalans, who say it tramples on their linguistic and cultural identity. Now the Andaluces and even the Canary Islanders have joined them in rejecting the plan.
Perhaps more than most Europeans, Spaniards tend to put regional loyalties above their loyalty to their country, which is hardly surprising in a land where regions have pushed around the people of other regions for more than a millennium.
The minister's proposal seems a curious volte-face in Spain, which has for some 20 years established a more-or-less harmonious relationship between 17 autonomous regions and the authorities in Madrid. This was achieved through a pragmatic experiment in home rule that handed out varying dollops of devolved power. The parcels of power varied in size according to the decibel-level of nationalist screams from the regions, so the Catalans, the Basques and the Galicians got most, including the right to determine 45 per cent of their school curriculum.
Fundamental was the recognition that cultural and political references common to all Spaniards don't have to be identical. This understanding lay behind the democratic constitution of 1978, which sought for the first time to embody a consensus, rather than to impose the vision of one half of the country upon the other. The aim was to overcome the fear, resentment and lust for revenge created during 40 years of Franco's dictatorship - which everyone realised could have torpedoed the democratic transition from the start.
Translated into the history lesson, this meant that King Ferdinand and Queen Isabella, whose expulsion of the last Moorish king from Granada in 1492 was conventionally depicted as the climax of a predestined process of unification, were now seen as the forgers of a new European state, bullying a clutch of independent nations into line.
The only "unitary" aspect of this clash of interpretations is the names, the dates and the battles. The real stuff: who did what to whom, who benefited and who suffered, takes on a completely different shape according to where you are standing. Regional spin doctors, free for the first time in generations, sometimes centuries, to write their own story, naturally spin it to their own advantage.
So, depending on where in Spain children go to school, they might learn that Ferdinand was a King of Aragon who, through a shrewd marriage, came to rule Spain. Or a Spanish king who ruled Catalonia. Or a sprig of the Castilian aristocracy who inherited the Aragonese crown. Or that the kingdom of Aragon was based in Catalonia, and that his name was actually Ferran.
The Catalans now scent the dead hand of authoritarian Castile trying to turn the clock back to the days when Castilian monarchs regarded Catalonia as a possession whose wishes could be ignored. The minister's big mistake was to have announced her new rules without regard to the Catalans' ancient oath to their monarch that still governs their approach to political pacts today. This is the sacred principle of "If not, not": "We who are as good as you, swear to you, who are no better than us, to accept you as our king and sovereign lord, provided you observe all our liberties and laws - but if not, not". Catalans don't want a decree, they want a treaty.
People's identity is forged by how they perceive their forebears were treated, and Catalans have no objection to being Spaniards (albeit, in their opinion, a superior kind of Spaniard) if they are allowed to be Catalan. When the Catalan leader Jordi Pujol told Mrs Aguirre that he would find it "impossible" to implement her "one-sided vision", he meant that she was breaking the pact and inviting confrontation. The Basques, who for centuries subjected their rulers to similar strictures beneath the ancient oaktree of Guernica, thought the same.
The "if not, not" principle also underlines the sense in Spain's regions that their democratic habits and institutions are stronger and more deeply rooted than those of the centre. Castile, which has never had a great reputation for tolerance or democracy, is described by the historian JH Elliott as "supine and priest-ridden" for much of Spain's golden age.
Hence, in a particularly clumsy step, the minister has stumbled over one of the two major fault-lines that has cleft Spain down the years: between the regions and the centre. And she has managed to weld together, in opposition to her, the other important split - between the political right and left. While the Conservative rulers of Catalonia and the Basque country complain that she is ignoring their national heritage, the southern Socialists accuse her of imposing a fascist agenda.
Within the ruling Popular Party are those who cling to the ideal of a centralised Spain, united and undivided, that was so dear to Franco; they hold that this devolution lark has gone too far. In a startling transformation, the party suddenly came over all autonomy-friendly the moment it won general elections in March last year and realised it needed Catalan and Basque MPs to form a government. Many couldn't stomach it.
Mrs Aguirre, stunned by the force of opposition to her plan, is swiftly rewriting her own history. She is open to suggestions, she says. It is only a draft for consultation. Perhaps the word "unitary" was "unfortunate". If anyone wants to substitute the word "common", she'd go along.
If history is written by the winners, Spain's ruling party will have to wait until it has an absolute majority before issuing new textbooks. Even then, it will probably find that any attempt to squeeze the toothpaste of autonomy back into the tube would provoke the kind of national revolts that most Spaniards thought they had consigned to history.