Encyclopaedia Britannica Inc. apologized Wednesday for mangling the history of the Irish Civil War, a longtime screw-up detected only this year when an Internet version of the reference book was supplied to Ireland's 4,000 schools.

"We do respond very quickly and our editors have been up all night looking at this," said Ian Grant, managing director of the company that publishes the world's oldest encyclopaedia. "It's important to get this thing right."

A concise version of the Britannica first published seven years ago and used initially on hand-held devices has falsely described Ireland's 1922-23 civil war as a fight between the Catholic south and Protestant north.

In reality, the civil war took place entirely south of the border, between two groups of Irish Catholic nationalists. The opposing sides were the fledgling army of the newly formed Irish Free State, which supported the Anglo-Irish treaty that created the state, and rebels who rejected it for failing to deliver full-fledged independence. The Irish Free State evolved over decades into today's Republic of Ireland.

Students quickly spotted the glaring error after the Irish Department of Education struck a deal to provide the Britannica's online version to all schools in the state. The contract costs a reported $625,000 a year for annual access to the encyclopedia and the publisher's other online references.

"This screwy version of events is a gross insult to our people and our history. That it is being used to educate our children is even more ridiculous," Irish Sen. Fidelma Healy Eames told the Irish Independent. The Dublin newspaper first reported the story Wednesday.

The civil war — in which Michael Collins' pro-treaty army defeated the rebels backed by future Prime Minister and President Eamon de Valera — has cast a profound shadow over Irish political life for decades.

Collins, slain in a November 1922 ambush by former Irish Republican Army comrades, is still mourned by many as Ireland's "lost leader." The country's two main political parties trace their origins to opposite sides of the struggle.

IRA die-hards rejected the treaty establishing the Irish Free State because Britain required the new state to remain within the British Empire, its elected officials to make an oath of fidelity to the British monarchy, and its ports to permit Royal Navy access. The anti-treaty side demanded total separation from Britain, while Collins argued that the treaty offered the maximum possible at that time and gave Irish nationalists "the freedom to achieve freedom."

But the war's true motives are frequently mangled by writers and commentators worldwide, reflecting today's focus on the continuing conflict in neighboring Northern Ireland.

The most common error is to attribute the Irish Civil War to Ireland's partition, when this issue was far down the list of rebel grievances. Britain had already partitioned Ireland before the treaty was even negotiated.

In an ironic footnote, British media reports that chided the encyclopedia Wednesday for its error demonstrated their own ignorance of the Irish Civil War. The British agency Press Association described the war as a "fight over the partition of Ireland."