You should just see what happens when international history buffs get together at a major hub like the All Empires forum.
It is certainly true that it is not always agreed if a certain event happened.
Post 500 BC or though however, most people agree on the course of major events and campaigns. There is no real doubt that the Julius Caesar conquered Gaul, or that the Battle of Kosovo happened in 1389. It is true that we do not know other military and physical details, such as where the Legio IX Hispania was destroyed or how many people were in the Ottoman army at the said battle. Most of the time however, no one really gets that worked up about it, everyone admits that Rome lost a legion on the borders now and then and that the ottomans crushed the Serbian kingdom.
When the fun really begins is culture. Is Montenegro culturally Serbian, or are Montenegrians (sp?) culturally independent? Or worst eastern Anatolia, was it "historically" Kurdish or Turkish? I've heard Kurds accuse the Turkish government of propaganda for putting descriptions of old folk songs sung in Turkish under an Eastern Anatolian label.
And were the Romans evil aggressors who destroyed the happy free Celtic culture of Gaul or noble bearers of the white man's burden and Roman culture, who spread the benefits of civilization to backward heathen? Few phrase it so bluntly, and if they do they get chucked out as trolls, but it comes up in things like the material culture of the pre-Roman Celts. Not to mention the never-ending "my ancestor could've kicked your ansestors butts" conversations. Just see the Han dynasty China vs Roman thread at the Chinese history forum.
In summary, unless you are talkling about every long time ago, the main events are well known in the general sense, and the particulars are not the matter of bitter contention most of the time. More subjective matters, particularly the spread and relative value of various nations/cultures is in my experience where the fun really begins.
