In the modern American lexicon, the Donner Party is synonymous with cannibalism. The average person knows next to nothing about these people or what drove them to do what they did, but everyone seems to know the one detail that matters: They ate each other. The actual truth is more nuanced than that, but there's no getting around that the story of the Donner Party is one of the most infamous examples of cannibalism in human history.
Ethan Rarick's Desperate Passage starts at the very beginning, at the head of the California Trail in Independence, Missouri. It was May 1846 and, as the pioneers of the time knew, that was an awfully late start date for a wagon party heading west. The risk of winter arriving before they did was too high. This was the first of series of unfortunate decisions that would, compounded over time, lead the emigrants towards historical notoriety.
Two points jumped out at me while I was reading. (1) To be trapped in the mountains during the early winter of 1846 under the circumstances that led to, not immediate death, but cannibalism was a result of an improbable confluence of timing. It's like the stars aligned in the worst way—geographic terrain, time of year, etc. Each factor had a small window that could lead to big problems and in each case the timing was disastrously perfect. (2) The Donner story is one of extraordinary actions under unimaginably desperate conditions, and yet the tale that people told for half a century afterwards painted the survivors as monsters. Why the lack of sympathy? Rarick supposes when sharing stories of westward expansion, of manifest destiny in other words, the storytellers preferred optimism over despair. The tragedy occurred just a few years ahead of the California Gold Rush and it's not hard to imagine that pioneers wanted reasons to push onward, not to stay away.