We appear to have an accurate claim for "greatest one-day spree killing total by a lone American civilian on an American school campus." This isn't nearly as good a headline, and it avoids the multiple-hundred-year-long context of mass violence as a means of "solving" problems. Clearly and obviously there have been much worse shooting sprees in our history. Note that we also have to modify the phrase to include "American," seeing as at least one other sick individual did worse in Australia, and that the worst a civilian American did in one day to this point was in a mosque in Israel. Those are just off the top of my head.
If we look to American "shooting rampages" against civilians abroad, we can of course point to My Lai...
As the "search and destroy" mission unfolded, it soon degenerated into the massacre of over 300 apparently unarmed civilians including women, children, and the elderly. Calley ordered his men to enter the village firing, though there had been no report of opposing fire. According to eyewitness reports offered after the event, several old men were bayoneted, praying women and children were shot in the back of the head, and at least one girl was raped and then killed. For his part, Calley was said to have rounded up a group of the villagers, ordered them into a ditch, and mowed them down in a fury of machine gun fire.This is, of course, just what we know about. There was also the American shooting rampage in the Philippines:
Other notable American rampages by those not in uniform would include the 1857 Mountain Meadows Massacre, in which about 120 non-Mormon white settlers were killed by Mormons who blamed "Injuns," with about a third of them merely bashed with rocks instead of shot, which should please those not wild about the 2nd Amendment. We could note the 1921 Tulsa Race Riot, in which it is claimed as many as 301 people were killed, mostly African-Americans shot by whites, although some non-gun lynching and burning occurred as well, and thousands of African-Americans were driven from their homes.
For its part, the U.S. Army was determined to crush further resistance in Samar by sending a veteran of the savage Plains Wars against the American Indians, General "Roaring Jake" Smith
Arriving on Samar, Smith, 66, tells his men: "I want no prisoners. I want you to kill and burn. The more you kill and burn, the more it will please me."
Asked the age limit, the general replies: "Ten years and older. The interior of Samar must be made a howling wilderness."
In the ensuing months, hundreds of villages are burned, all crops and livestock destroyed. Thousands of Filipinos are shot as suspected rebels. Other civilians are rounded up and put in "concentration camps" -- so called because they are "concentrated" into a small area making it easier to guard. ... Exact figures of how many Filipinos were killed in Samar were never made public. But it is estimated that 10,000 were killed or starved to death over a two-year period following the massacre, the majority women and children.
For domestic extermination of "subhuman" tribals we could point to the 1863 Bear River Massacre ... in fact, let's do just that:
Approximately 250 Shoshoni were slain, including 90 women and children. After the slaughter ended, some of the undisciplined soldiers went through the Indian village raping women and using axes to bash in the heads of women and children who were already dying of wounds.It'd do us well to review the long record of mass killing sprees on both sides of the conflict; here's a list of some major Indian massacres, both against and by the Native population. Note that over 300 people were killed at Wounded Knee alone.
More recently we could review the 1992 L.A. riot, in which more than 50 people were killed. Could we forget that already? This sort of thing has happened frequently enough that there's a two-volume Encyclopedia of American Race Riots. Some of them had hundreds of deaths, such as the Wilmington (NC) riot of 1898.
Even limiting ourselves to individual killers, we must categorize this outburst with spree killers and not serial or mass killers, many of whom claimed far more victims as a cursory examination of the facts displays.