Over the past few decades, alternate history has emerged as an increasingly popular sub-genre of science fiction. Through it, an ever-growing number of authors and fans have postulated the different turns that history might have taken, often because of relatively minor circumstances. Most writers use this to establish a divergent setting for fictional works, in which characters come to terms with the very different worlds that emerged as a result.
In this respect Robert Sobel offers something different. Rather than develop an alternate history setting for a work of fiction, he created something far more elaborate - a thoroughly articulated timeline of events resulting from a British victory in the Battle of Saratoga. From it, he envisages an American Revolution that ends in a British victory and the emergence of two different countries - the British-spawned Confederation of North America and a separate state founded by the surviving revolutionaries that evolves into the United States of Mexico.
A prominent business historian, Sobel presents his alternate history in the form of a "nonfiction" text rather than that of a novel. This is a considerable undertaking; instead of simply drafting a setting, he has to develop an increasingly intricate sequence of events, all of which must be plausible in explaining broader developments that took place over the following two centuries. Adding to the challenge is that he does this within the context of a narrative "history" without the benefit of the novelist's devices of character and dialogue to maintain the reader's interest.
All of this makes Sobel's achievement an impressive one. Not only does he present a plausible and fully realized alternative to the history with which readers will be familiar, he does so in a way that can keep a reader's attention. In many respects, it reads as a satire of a true nonfiction work, complete with footnotes citing nonexistent books and fake disputes between academics who never lived. It serves as just one more strata of a richly-layered work, one that may not be as exciting of a read as the works of authors like Harry Turtledove but one that can envelop the reader in a way that few other works of the genre are able.