Age of Empires 2 gets a lot of things wrong mainly for the purpose of gameplay and to create a cohesive narrative.

For instance, William Wallace and the Scots lost the Battle of Falkirk, and the game depicts Wallace as remaining as the head of the Scottish forces even though he resigned after the Battle.

Saladin lost the Siege of Acre, and the siege in gameplay is inaccurately depicted. If the game had been correct, Saladin would be in a camp surrounding the Crusader's camp, who would be camped surrounding Acre. Saladin was attempting to crack the Crusaders before they cracked Acre. Also, egregious are the weapons fielded in that battle; the Frankish faction uses Bombard Cannons way before they became a viable weapon, Richard using Longbowmen instead of Crossbowmen like he did in real life, but that's being nitpicky I guess.

In the Ghengis Khan campaign, the 3rd mission pits the player vs 4 Chinese factions. The Xi Xia, the Tanguts, the Jin, and the Song. Well, first of all "Xi Xia" is the name of the dynasty and the ruling ethnic group of that dynasty were the Tanguts. Jin and Song are the names of their dynasties, so that's correct (imagine having to fight the Jin AND the "Jurchens," and the "Han" AND the Song) but the Mongols did not defeat the Song Dynasty until much later and after Ghengis' death. Actually the campaign in China lasted for generations of Mongol rulers, but the game neatly ties it up into only one scenario while devoting 2 and 1/2 missions to their European campaigns.

The 2nd mission is pretty weird, too, as it depicts the Kara-Khitai and Kushlug as simply being allies up until Ghengis kills Kushlug. In real life, Kushlug usurped the ruler of the Kara-Khitai so they should have just been one faction.

The 4th mission shows Ghengis ostensibly provoking the Shah in a weird retelling of what actually happened: Mongol traders came to a city in Khwarezm but were arrested by the governor of that city. Ghengis sent 3 of his ambassadors to the Shah, who then proceeded to execute those dudes and the traders. The Shah survived the initial destruction of Khwarezm and fled to modern-day Pakistan and was killed there, instead of being assassinated before the invasion.

Also the ending of Ghengis Khan's campaign pretty much says the Mongols conquered Europe and Asia, and shows a map that puts the entirety of Europe in the Mongol Empire's borders. In real life, the Mongols did not advance much more after the Battle of Sajo, the 6th mission.

Barbarossa's 1st mission shows a very simplified version of what Barbarossa actually had to do in real life. Barbarossa was the Duke of Swabia, so it makes no sense for him to have to fight Swabia. The other Holy Roman states depicted in the mission came under Barbarossa's sway peacefully through marriages and alliances, and some of these alliances happened AFTER Barbarossa's campaign in Italy.

Barbarossa never went to war with Henry the Lion. He never betrayed Barbarossa in Poland and in fact Barbarossa didn't do a whole lot in Poland, expansion into Poland was Henry's project. Barbarossa went to Italy like 4 times and Henry the Lion didn't betray him, he just didn't send soldiers to Barbarossa like he asked.

Furthermore, Barbarossa's remains never touched Jerusalem. He also never had to besiege Constantinople and fight it's army then hijack it's Navy. Threatening the Hagia Sophia is not based on real events.

Ignoring gameplay constraints such as maps, weapons used, civilization choices to represent certain factions, and absence of possible story elements, Attila is mostly accurate if only because the sources on the Huns during this time are pretty scant.

Montezuma is mostly accurate. The 1st and 2nd missions don't seem to be based on any particular historical event, BUT Tlacopan and Texcoco did not betray the Aztecs until after the Spaniards arrived in Mexico. Also Cuauhtemoc, the narrator, should not have ascended the throne until just before the 6th mission, the Siege of Tenochtitlan. The game claims he became Emperor right after La Noche Triste when in fact Cuitláhuac, Montezuma's younger brother and also Cuauhtemoc's uncle, would have been Emperor at the time.

Other inaccuracies that I can think of off the top of my head:

• Harald Hardraade offering an alliance to William of Normandy. The game depicts the Battle of Stamford Bridge but leaves Harald out of that battle. Also, there weren't any Saxon Raiders in Normandy because Harald's invasion was a much bigger deal than shown in game and Harold Godwinson had his hands too full to send a counter-invasion into Normandy.

• The Koreans did not stage a counter invasion of Japan like the game makes you in Noryang.

• Henry V successfully captured Harfleur, whereas the game outright says "The Siege of Harfleur is lost. We must retreat to England."

• Guy Josselyne is a character made up by one of the game developers, Sandy Peterson, based on his far-flung, minor noble ancestor.

• The Burgundians were not present for the Battle of Orleans, nor were they present for the Battle of Castillion, the 6th Joan of Arc mission.

• Most of the game's objectives do not have any basis in history but I'd like to think that's obvious. Ghengis Khan did not conquer Poland, Bohemia, and Germany by playing capture the flag with them, and Don Juan did not construct a gigantic replica of Toro del Oro somewhere on the shores of Greece in order to shock the Ottomans into losing the Battle of Lepanto.

Sorry, this went on way longer than I thought. I have diarrhea of the fingers.

We often get questions about the historicity of the Civilization games, and a common criticism is the tech tree: a linear progression from "primitive" to "advanced" that's only vaguely accurate for European civs. You can't get anywhere in the game without writing, horseback riding, and the like. Age of Empires does have some historical merit in this regard. Each civ has it's own tech progression. If you're the Aztec, you can be a viable force w/o horses; you're not stuck to a Westernized progression of civilization.