Assassin's Creed on the whole gets credit for being slightly more accurate than usual, as far as video games go. Bear in mind this is "slightly more accurate than usual" by video game standards, so there are still dollops of Artistic License. On the whole the series sits comfortably between Alternate Universe and Like Reality Unless Noted. It uses the rhetoric of historical revisionism to justify the inclusion and insertion of fictional Assassins and Templars into a historical context, justifying their presence by stating that modern day Templars have modified history to hide the truth. On the other hand, historical events and figures largely do act the way they did in a certain time and place and the backgrounds are generally accurate, with some of the details being Shown Their Work on the part of developers.
Assassin's Creed I gives a vision of The Crusades modified into a fight between The Knights Templar and The Hashshashin, neither of them being religious orders as we know them from history, but proto-secular humanist secret societies who fight over the use and abuse of Magitek artifacts left by Precursors. In reality, the Templars had the mundane duty of safeguarding the lives and possessions of travellers journeying to the Holy Land, the Assassins mostly attacked local rulers and corrupt officials and never came into conflict with the Templars. The game does provide a more nuanced look at Richard the Lionheart than usual, however, notably having him speak in a French accentnote Historically, Richard I spent little time in England and most of his life in Angevin France, and likewise does portray the Hashshashin as "the Asasiyun", demolishing the hashish-smoking Hollywood History.
Assassin's Creed: Brotherhood started introducing Baroque architecture into the Renaissance, features workable Da Vinci machines, and presents a fantastic internal La Résistance against Cesare Borgia that needless to say goes against actual history. Assassin's Creed: Revelations also anachronistically calls the fallen Eastern Roman Empire as "the Byzantines" though it generally does get some features of the Ottoman Empire correct, showing them as a multi-cultural society with a good look at the fratricidal politics of the Ottoman Empire's Deadly Decadent Court and the manoeuvering of the Janisarry Praetorian Guard. Architecturally it avoids anachronism except for providing Hagia Sophia minarets far earlier than recorded.
Assassin's Creed III was praised for its broadly accurate chart of the American Revolution, background and causes. Some of the Artistic License however is that nearly everything about the game's depiction of the Boston Tea Party is wrong. The game depicts it as a riot in which a few dozen British soldiers get killed when it was in fact a non-violent incident; also, Robert Faulkner, the First Mate, makes references to Singapore, which had fallen into obscurity centuries before. The gameplay also moves ahead certain activities (Fort liberation) earlier than the context would allow. It also features a Historical Villain Upgrade of Charles Lee, though it does put forth the shortcomings and hypocrisy of the founding fathers, in one extent going a bit too far by attributing the destruction of Connor's village to George Washington... in 1761, a whole three years after Washington retired from the military.
Assassin's Creed IV: Black Flag was likewise praised by historians for a more nuanced look at the pirate era, though the gameplay's violent approach to naval combat was far away from how pirates actually operated, and it still made some odd changes. In real life, Mary Read used and was raised under a male persona based on her late older brother, Mark Read. In Black Flag, her disguise is inexplicably changed to that of James Kidd, supposedly an illegitimate son of the historical William Kidd. This is lampshaded in the codex, where an entry on a landmark has the art director comment that it hadn't been constructed at the time the game took place. The producer tells him to put it in anyway.
Possibly to atone for Unity, Assassin's Creed: Syndicate's artistic license comes with a healthy dose of Refuge in Audacity, such as exaggerating the extent of Victorian London's criminal underworld to create, essentially, Grand Theft Auto: Industrial Revolution. The game also transplants aesthetics from other "Gangland" works onto the Victorian setting (ranging from the almost-contemporaneous Gangs of New York to 1960s' Swinging London).
Assassin's Creed Origins: There are a lot of little things the game gets wrong, but for the most part it was praised for its accuracy. The biggest mistakes mostly revolve around Cleopatra and her relationship with Caesar, which was more controversial in real life than it is portrayed in the game.
Part of the backstory for Killer7 involves an elementary school that has decided who the president of the United States would be since George Washington, located in Seattle, Washington. At the time of Washington's presidency, Seattle didn't exist, only populated by the tribes already living in the area. Seattle wouldn't be founded until 1851, sixty two years after Washington's election. Even with the extremely bizarre nature of the game, there is no reason to make such a mistake.
Imperium Romanum has a scenario set in 132 BC. The very first words of the description claim that Augustus Caesar currently has a firm hold on Rome as the first Emperor. This is off by more than a hundred years: Julius Caesar (let alone his adoptive son Augustus) hadn't even been born yet. This is not hard to notice if you're aware of the widely known fact that Julius Caesar was assassinated in 44 BC.
God of War didn't even try to portray Kratos realistically, it seems. To give one example, he was bald. Real soldiers of that time period wore their hair long, and were very proud of it, doing their best to keep it groomed.
In the 2006 E3 press conference, Genji was advertised as being "historically accurate". A minute or so after the spokesperson said this, his player character was attacked by a Giant Enemy Crab, right as the spokesman claimed that the game features "famous battles which actually took place in Ancient Japan". It was poked fun at in Sony's E3 2013 press conference - an indie developer stopped while describing his game and said, "and while historically accurate, it doesn't feature any Giant Enemy Crabs".
Used in-game in BioShock Infinite. The citizens of Columbia venerate the Founding Fathers (Washington, Jefferson, and Franklin) as prophets and messiahs, while in reality, they would have been appalled at the fanaticism, oppression, racism, elitism, and abuse of power the Columbians preach and practice. (Jefferson established the "separation of church and state", Franklin protested against the caste system and was a deist to boot, and Washington was racially and religiously tolerant, and is against a permanent office position.)
All the Civilization games seem to think that Persia historically ended with Alexander's conquest. In reality, there was a country called Persia right up until 1935. After that date it was called by its native name, Iran.
The creators of Ryse: Son of Rome, Crytek, have admitted to not be aiming for historical accuracy with their game. It certainly shows when Boudicca sacks Rome with war elephantsnote Boudicca's insurrection was limited to what is now known as England, and while she did sack a city, it was Camulodunum (now Colchester), not Rome. And oh boy, did she ever not have elephants. And the historical silliness doesn't stop there.
The narration in Onimusha: Warlords says that Tokichiro will eventually go on to conquer the entire world under a different name. Uh...sure, if by the world you mean the majority of Japan.
Paradox Interactive by and large did its research, so the starting scenarios are reasonably historically accurate (see below), but AI rulers tend to have little if any interest in directly mimicking the behavior of their historical counterparts, never mind player-created insanity such as a Slavic Empire ruling the Holy Land.
Particularly in earlier start dates, the lack of accurate records for many regions means that even the most dubious dynastic lineages, from 90% of Swedish rulers claiming descent from the legendary Viking Ragnar Lodbrok to Irish counts insisting they were spawned by Conn of the Hundred Battles, are given the benefit of the doubt by the developers. Ragnar even becomes a playable character with the CharlemagneDLC's 769 AD start. Paradox didn't have much choice here: the alternative in many cases was to make people up entirely (and in the time periods in question, people really did take these kinds of claims seriously). Still, several playable early Yemeni rulers are known to be completely fictional. Another license with the earlier start days is back-projection from the original start-date (1066), mostly of things where simulating the historic development would be complicated and require significant investment of development time and effort (the most prominent example is probably that the Catholic and Orthodox churches are portrayed as already existing).
Historically, when a Mongol Great Khan died, all other Mongol military activity was to cease and the leaders were obliged to return with their armies to Mongolia to see the "election" of the successor. This was one of the only things that saved Western Europe from annihilation when Ogedei Khan died in 1241. This rule does not apply to the Mongols in either Crusader Kings game, even when other such unusual succession behavior such as Muslim open succession is kept.
Eiyuu Senki: The World Conquest not only has numerous historical figures interacting with each other beyond the limits of both time and fiction- King Arthur meeting Billy the Kid for example- but every single one of them in that universe is a woman.
For all Onmyōji has shown about Onmyōdō and Japanese myths, there are many liberties taken in its portrayal of the Heian period for reasons such as Rule of Cool or Rule of Sexy. Examples include most clothings' being way ahead of their time, except for maybe Seimei'snote and even his clothing is very stylized, the fact that only a handful of characters speak using the region's dialect or archaic vocabulary. There are also characters who walk around with kiseru pipes in hand even though tobacco wasn't yet introduced to Japan in this time period as well as a line of dialogue and, in the all-Japanese version, a skill's name containing English words.
The game's portrayal of the historical figure Minamoto no Hiromasa as primarily a Mage Marksman rather than a musician (even though he's still shown to play the flute) should also be taken into account. And the fact that he's given a sister whose name is not Kenshinote no, not the Fujiwara one and none of his real-life brothers are given a mention.
Apparently Kamo no Yasunori does not exist and Seimei was introduced to onmyōdō by his mother.
There is a type of mitama called Shami (shamisen) featuring the three-stringed instrument on its icon and Mōba who even carries a very stylized version of one (and constantly plucks it by hand) even though, you guessed it, it wasn't yet invented in this period.
In Rome: Total War, Egypt fields a number of units that look straight from the New Kingdom, i.e, several centuries before the game is set. The developers acknowledged that the faction's appearance and unit selection were anachronistic but said it was a deliberate choice to avoid them being too similar to other factions. One popular conversion mod, Europa Barbarorum, converts the Egyptian faction to be more authentic, as a Macedonian/Greek inspired faction. Also, we're pretty sure the ancient Britons didn't throw severed heads at their enemies.
While Scotland historically was relatively poor and isolated, it was a feudal nation which fielded men-at-arms and knights just like any other European nation at the time - most of the fighting men were recruited from the lowlands and borders. Of course, this is not the case in Medieval 2, where Scotland is Braveheart Land and every soldier is a highlander is wrapped in a kilt (which wasn't around back then) and has blue woad all over his face.
Helsinki is portrayed as a castle and the capital of Finland. Not only did Finland not exist as an entity at the time, but Helsinki was just a simple fishing village.
England's generals, princesses and ruling family members all have Anglo-Saxon names and speak English with a familiar English accent. The real-life Plantagenet dynasty would never have used Anglo-Saxon names, and every single monarch in England from 1066 to 1399 spoke French as their first language.
Being able to conquer all of Ireland simply by taking Dublin is a gross oversimplification. The Irish resisted the English with the utmost ferocity and it took four centuries of near-constant war for the latter to establish political control over the entire island. The Britannia expansion remedies this by splitting Ireland into eight provinces (and Wales, four).
In Empire: Total War, Moscow is the capital of Russia. Historically, St. Petersburg was the capital from 1713 to 1918. The Winter Palace and the Kunstkamera museum, both in St. Petersburg in real life, can only be built in Moscow in the game.
In Total War: Shogun 2, the Boshin War of 1868 can be a titanic conflict which can last years, rack up a death toll similar to that of the American Civil War (600,000 lives lost through various causes) and involve troops from the United States and the British Empire. In reality, it was just a small-scale conflict which ended with 3,500 deaths.
In Total War: Attila, it's possible to meet a Germanic tribe which worships Tengriism decades before the Huns ever really arrived in Europe in real life. And the Visigoths were Christians, not pagan.
Nioh features early modern plate armor existing alongside high medieval greathelms and arming swords in the level which takes place in England.
Senua is said to be a Pict from Orkney, though she looks nothing like one. Her rawhide leather outfit gives off more of a fantastical Native American vibe, quite far removed from the colourful tunics, mantles and cloaks that the Picts wore.
Senua herself has a southern British name, her partner has a Welsh name, and her parents have fictional non-Celtic names.
Senua's sword's design and her society's reverence of severed heads are inspired by the continental Gauls, rather than the Picts.
Spartan: Total Warrior is explicitly stated to take place in 300 BC - and apparently Marcus Licinius Crassus, Lucius Aelius Sejanus, Emperor Tiberius, Archimedes, King Leonidas I and Beowulf are all contemporaries. Not only were none of them alive in 300 BC, one of them is mythological, and only two of them (Sejanus and Tiberius) even lived at the same time as each other. The blow is somewhat softened by the fact that the game is in no way portraying itself as a historical work; it's an action-packed hack-and-slash in the God of War vain, complete with magic, monsters, zombies and gods.