As of Sunday, the title of deadliest mass shooting in modern U.S. history is claimed by the horror in Las Vegas that left at least 50 people dead and hundreds more injured. Before the Vegas shooting, that grim honorific was held by 2016's Orlando nightclub shooting, in which 49 people were killed.
If it feels as if record-setting attacks are escalating faster than they used to, that's because they are. While violent crime overall is historically low, America’s mass shootings are getting deadlier, as The Washington Post shows in a graph plotting the spiking death tolls in mass shootings since 1949:

Between 1949 and 1991, the number of total deaths in any mass shooting increased by nine, from 14 killed in New Jersey in 1949 to 23 killed in Texas in 1991. From 1991 to 2017, however, the number of total deaths in any mass shooting increased by at least 27 — triple the growth over a shorter period of time.