Although there are exceptions (conspiracy theories, religious arguments, etc.), humanity has come to a consensus on what has happened in the past. The United States and the Soviet Union never nuked one another, the empire of Alexander the Great collapsed shortly after his untimely death, cross-Atlantic travel was technologically impossible until the late fifteenth century, and Nippon was an isolated nation until outside intervention inspired the rise of the Empire of Japan.
In the realms of science fiction & fantasy, however, liberties are sometimes taken with history to provide an alternate, "What if?" scenario. From Nazis with advanced technology to nuclear fallout across America, historical inaccuracy has a rich tradition in video games.
Games that contain historical inaccuracies sometimes do so blatantly. For example, the Assassin's Creed franchise introduces a long-running rivalry between the Templar and Assassin guilds. Both these factions are reported in game to have an enduring history, including ties with actual classical figures and worldwide governments. The Crimson Skies and Red Alert series both have alternate histories stemming from divergences in mid-twentieth century events, while Civilization games or titles in the steampunk genre may feature technological disparities or other anachronisms for gameplay or story purposes.
Games may also feature anachronistic elements due to incomplete research or poor writing. The game Godfather II features styles that were not yet present in the era it is depicting, while Rogue Warrior may have included pop-culture references that had not yet been popularized by the time period in which it is set.