The British government’s partition of India in August 1947 was a supremely bungled event: undertaken at high speed and with apparently zero foresight. Speaking to journalists about the possibility of a mass transfer of populations across the border, the viceroy of India said, “Personally I don’t see it.” This was two months before partition. Sir Cyril Radcliffe, who drew the borders of Bengal and Punjab, infamously did so on his first and only visit to the country. All said, some 12 million people were displaced and 1 million killed in the aftermath of partition. Overwhelmed by refugees, the two newly created nations of India and Pakistan retreated into a routine of patriotic rhetoric.

The rhetoric continues today. Depending on the state of diplomatic rapport between the countries, it can be ridiculous (Indian and Pakistan are congenital enemies), romantic (India and Pakistan are two sides of the same colonial coin), or even pseudo-surgical (India and Pakistan are Siamese twins severed at birth in a botched operation). As a result, the men and women who died in partition have become martyrs for a metaphor; their haplessness and ambivalence have been slowly forgotten.

Yasmin Khan’s excellent book “The Great Partition: The Making of India and Pakistan” (Yale University Press, 210 pages, $30) attempts to expose the dangers of such forgetting and to unlace the great ambiguities that characterized the years immediately before and after independence. Ms. Khan succeeds admirably. She is adept at laying small, human-sized stories side by side in parallel tracks, and her thesis steams along cleanly as a result. At 210 pages, the book is wonderfully compressed, both a primer and a historical correction. The horrors of partition and the callousness of the British have been well documented in books and film; what is less known, Ms. Khan argues, is the level of confusion — at every conceivable level — that accompanied the violence. The viceroy of India was hardly alone in his naïveté. Many assumed India and Pakistan would continue with soft, visa-free borders. Damningly, those lines weren’t announced until August 17, 1947, two full days after India’s independence. Much of the rural populace didn’t even hear about the contours of the border until much later.

Right from the outset, the drawing-room simplicity of the plan was at odds with the messy diversity of India. How, for example, to account for Muslims in parts of India that weren’t Bengal and Punjab? Or minority groups in the new Muslim homeland of Pakistan? Worse, Khan writes, “[s]maller groups such as ‘untouchables,’ Christians and Anglo-Indians were simply pushed aside by the sweeping plan.” Most Sikhs chose to stay in India, but the birthplace of Guru Nanak — the founding guru of Sikhism — fell irretrievably in Pakistan. The poor fared the worst across the board. The writer Fikr Taunsvi recollects how a washerman, wishing to feed his newborn baby, couldn’t do so because Muslim milk-sellers were afraid to step into a Hindu area. Further, the call for division was at times almost comically enacted by civil servants: While Muslims and Hindus notched up all manners of creative atrocities against each other, a librarian in Delhi allocated alternate volumes of a single set of the Encyclopedia Britannica to India and Pakistan.

The book is sustained by such fantastic weaving. We may briefly glimpse Mohammed Jinnah — the father of modern Pakistan — admitting in an editorial letter, “It is very difficult for me to understand what led his His Majesty’s Government to come to the conclusion of partitioning Punjab and Bengal,” or Jawaharlal Nehru — India’s first Prime minister — making his famous “tryst with destiny” speech. But always we are swept back to the streetlevel mobs and mayhem.

This technique is especially effective in explaining the sources of partition’s violence. “The black and white imagery of ragged refugees and bloodthirsty peasants should be replaced,” Ms. Khan argues, “with a technicolour picture of modern weaponry, strategic planning and political rhetoric.” The violence of partition was the sum total of many tiny pogroms; the spontaneous emergence of these pogroms at once has been mistaken for a spontaneous emergence of violence in general. But such violence does not emerge overnight.

In the end, both British and Indian politicians are to blame, particularly in Punjab: the British for dismantling the army and leaving a grossly ineffective Punjab Boundary Commission in its wake; local politicians for arming militia — with both weapons and ideology — in the ensuing vacuum. It is easy to see why Mahatma Gandhi refused to celebrate independence, urging that the day be reserved, instead, “for prayer and deep heart-searching.”

The violence of the period also fed on rumor and propaganda, and Ms. Khan presents us with numerous bombastic newspaper headlines and speech clips that helped fan the flames. Unfortunately, “The Great Partition” itself suffers from overwriting, repetition and bad editing. “The best have turned the emptiness of this moment into poetry, and grown new creative life into the hollow abyss of Partition’s worst moments,” Ms. Khan writes of the literature of partition, and it is hard not to feel that you yourself have fallen into one such abyss — albeit a literary one.

Speckles of writerly carelessness in an otherwise excellent work make one wonder if the publication of “The Great Partition” was rushed to coincide with the 60th anniversary of partition. If so, there is an unexpected fringe benefit: The book appears at a time when American legislators, led by Senator Biden, are pushing for the partition of Iraq along sectarian lines. Of course, the situation in pre-independence India and post-invasion Iraq are far from analogous. But these politicians would be well advised to remember that a similar intent was behind India’s partition. A year before independence, when Bengal was imploding in religious riots, many actually believed partition would put an end to the infighting.

The events of August 1947 and the years after vividly overturned that hypothesis. For 60 years, Indians and Pakistanis have been living in suspicion of each other while simultaneously ignoring the lessons of their sundering: Divisions only foster further divisions and quick-fixes are disastrous for complex situations. Fittingly, there is only one memorial to the victims of partition in India: the Martyr’s Memorial in Chandigarh. And even this monument forces one to ask: Who was martyred, and for what, exactly?

Mr. Mahajan is a writer living in Manhattan. His first novel, “Family Planning,” will be published by HarperCollins next year.