There's a delicious moment in Alan Bennett's play "The History Boys," when the class jock admits that he hates reading history because "it's just one f— thing after another." The line always gets a roar of approval from the audience, suggesting that it isn't just students who feel let down by the subject.

Mindful of those roars, I was determined that my book on British involvement in the American Civil War would not become a mere shopping list of events. I also wanted to avoid that tedious literary device of "meanwhile, back at the ranch…." Nothing is more trying for a reader than being taken on never-ending detours.

Unfortunately, the fruit of my 11 years of research meant that I had more than 400 characters scattered over four regions: Europe, the Union North, the Confederate South and Canada. Worse, their interactions with one another spanned several different spheres of war, from military and diplomatic affairs to social and cultural relations. This vast mass of material was so unwieldy that I could hardly work my way through the first day of the conflict, let alone all four years.

Having plotted the time lines of some 400 farflung characters, I shed more than half of them.

I knew I wanted to write a "history-in-the-round," where the reader is immersed in the narrative, rather than simply encouraged to follow it. So I decided to construct the outline of the book as though it were a musical score, with each character assigned an instrument. I could then develop the broad themes of the book across the entire "orchestra."

To do that, I first had to impose order on a cacophony of unrelated narratives. I plotted the time lines of my 400 characters and identified and discarded people who, no matter how interesting their stories, had no connection to anyone else in the book. This winnowed my cast down to 197 characters, all bound to one another by acquaintance or one degree of separation.

Next came the task of creating a linear narrative out of multiple, simultaneous events. I used the momentum of geography to give the impression of forward movement. For example, after describing the battle of Gettysburg from the point of view of several English observers and journalists, I followed their reports to London for a quick look at the British reaction. News of Gen. Meade's victory over Gen. Lee destroyed the last effort by the Confederacy to win recognition in Parliament, but the celebration at the U.S. Embassy was muted by the staff's puzzlement over the nonappearance of the weekly mail ship from New York.

The cause was the draft riots there—which allowed me to hurry across the Atlantic, just in time for Col. Arthur Fremantle (one of the English observers at Gettysburg) to witness the lynching of a black man by an Irish-led mob. Fremantle sought refuge at the British Consulate, where a desperate Consul Archibald was hourly cabling the Royal Navy for a warship to rescue black British crewmen under siege by the docks.

The dutiful consul remained at his post until peace was restored, but English merchants were unimpressed, complaining to the embassy in Washington about their lack of protection during the riots. The British ambassador was in a pickle...which brought my story back to Washington for the next military crisis.

Alan Bennett's punch line about the tedium of many historical narratives was first used by the Cambridge don Sir Herbert Butterfield. The truth is, most historians want to infuse their work with drama.

The great challenge is to combine evidence with art without sacrificing the integrity of either.

—Ms. Foreman's new book is "A World on Fire: Britain's Crucial Role in the American Civil War."