"Not an accident."
During this same period, settlers killed over 400 Native Americans. Again, that's not zero, but it does mean that the vast majority of settlers never got into a murderous conflict with hostile tribes. It was far more likely that the average settler would trade with Native Americans or hire members of various tribes as guides, rather than fight them. It wasn't necessarily because they were open-minded and peace loving that they abstained from violence, but rather that it's never good business to kill your customers, or vice versa. Especially when you're talking about someone providing a potentially life-saving service (a guide kept you from getting lost, when getting lost meant getting dead).
Native American deaths caused by the U.S. government and the military likely number in the millions. No one's disputing that one. But deaths due to wagon train clashes were few and far between. As for the "circling the wagons" thing, that ring formation was done each night not to keep hostile Indians out, but to keep their absurdly expensive cattle from wandering off. Hell, it wouldn't even be possible to "circle the wagons" in an emergency -- these wagon trains typically traveled spread out in a line several miles wide, rather than in the column that the term "train" suggests, in an effort to avoid each other's dust, wheel ruts, and debris. It would have taken hours to get everybody together and hooked up in circle formation.
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