@ami_angelwings Re alternate history:
1) to be good it has to do the actual work of world-building. I was disgusted by Sliders because each episode's premise sounded like something cooked up over a three-martini lunch ("the US lost the Korean War and by the 1990s thd USSR ruled the world"; "medical science never developed, but the rest of technology and commercial culture were exactly the same"; etc.) to provide some kind of general moral object lesson, without anybody doing the basic nuts and bolts work of constructing an plausible timeline from the point of divergence;
2) if someone could travel in time and alter even the most trivial of events in the past, none of the people born subsequently would be the same. There would not be analog Kirks, Spocks, Kiras, etc., as in the crossover episodes of Star Trek. The ripple effects of even briefly interacting with one person would cause minor changes in everyone's routines, eventually resulting not only a few minutes difference in arrival times, but missed meetings, which would snowball into more serious changes, etc. And altering the time when children were conceived by even a minute would result in different sperm fertilizing the egg, and a different random mix of the parents' DNA. The first generation of children might be born at roughly the same time and given the same names; but after that, while the general forces of history and tech might continue along similar lines, the specifics would be increasingly different.
By far the best example of due diligence I've ever seen in constructing a plausible alternate timeline is Poul Anderson's "The House of Sorrows." The POD is Jerusalem falling to Assyria in 723 BC, so Jewish monotheism -- and consequently Christianity and Islam -- never develops. The history of the Hellenistic and Roman empires is largely the same, but when the Roman Empire decays and the Germanic invasions begin there is no Church to preserve classical civilization or westernize the German tribes. Roughly the same kingdoms, under invading tribal aristocracies, arise on the ruins of the Western Empire. But with no Christianity or papacy, the Franks are just another kingdom -- no Holy Roman Empire, no Carolingian Renaissance, etc. The Byzantine Empire lasts about the same amount of time and eventually falls to a Turkish invasion from Central Asia, but with no Islam the Turks worship some kind of "Warrior Buddha." Etc.