Time travel is a plot device which has become a recognized staple of science fiction and fantasy. It involves sending people and/or objects from one time to another. No analog of time travel has ever been known to exist in documented reality.
Sometime between the 500th and 600th centuries, time travel permission was rationed out to certain individuals for a variety of reasons. For example, graduate student Lasoporp Rof was permitted to travel to 13th-century Mongolia to interview Genghis Khan. However, he mistakenly landed in 1980s Los Angeles in the office of a different Genghis Kahn.
Time travel was possible by 2014 in the original timeline whence the "Rivington Men" of "America Will Break" (a group of Afrikaner Weerstandsbeweging members) originated. The machine had a limitation in that it could send people and things exactly 150 years back and forward in time. In 2014 they stole a machine and imported men and materiels to 1864 to alter the course of the American Civil War.
The Rivington Men succeeded in creating a Confederate victory in the "Second American Revolution". However, they were unable to maintain their hold on the government in the post war years and rebelled. In the government's hunting down of the terrorists, all of the AWB men were killed or captured, and their time machine was destroyed in the battle.
Michelle Gordiantraveled from 1988 to 1949 to save America from its dark history in the intervening decades of the original timeline. By 1953, she had popularized several true stories of her world's 1960s and '70s in the form of pulp fiction, but history as a whole had not yet shown any appreciable signs of change.
In 1999, obscure Roman deities Liber and Libera were more than happy to grant Nicole Gunther's wish that she could live in the days whence they came, instead of modern Los Angeles. The two gods, taking the wish for a real prayer, obliged by sending Gunther to ancient Carnuntum, and placing her consciousness into the body of a local woman in the year 170.
After a year of living in the 2nd century, Gunther begged the two gods to return her to the 20. Though puzzled, as they regarded Roman times as much the better period of the two, the good-natured gods again granted her wish.
In 1963, disgusted with the idea that the Kennedy Administration had taken the nickname "Camelot", a young British druid named Duncan Morris cast a spell that sent Kennedy back in time to the original Camelot. Kennedy had an erotic misadventure in the past with Guinevere, wife of the absent King Arthur. Guinevere and Kennedy blackmailed Merlin the magician into sending Kennedy back to his own time, and he returned to the exact instant he had left.