Time Patrol

Between 1955 and 1995 Poul Anderson published a series of short stories, novelettes, novellas, and novels, about the Time Patrol, a secret group of people from all over the world whose job is to protect the world history we know. They jump up and down the timeline, making sure that terrorists and other disruptors don’t use time travel to remake history to suit their own malign purposes. Or any purposes, actually. Their goal is to keep history the same, even with all its evils, so as not to accidentally wipe out human civilization so that we can eventually evolve into the Danellians, a post-human species that is highly invested in making sure history doesn’t change.

It's a compilation of books [“Time Patrol” (1955, novelette), “Brave to Be a King” (1959, novelette), “Gibraltar Falls” (1975, short story), “The Only Game in Town” (1960, novelette), “Delenda Est” (1955, novelette), “Ivory, and Apes, and Peacocks” (1983, novella), “The Sorrow of Odin the Goth” (1983, novella), “Star of the Sea” (1991, novella), “The Year of the Ransom” (1988, novel), “Death and the Knight” (1995, novelette)]