Knowledge (history) deals with, obviously, history – modern (within the last 50 years); recent (50-500 years ago); and ancient (500+ years ago). Knowledge of history means the PC can give dates and locations of significant events, as well as who was involved and what happened. He may also know about the history of magic items or religious artifacts. The PC can specialize in one of the time periods noted above, or in a specific time period in history – the rise and fall of the Talenese Empire, for example.
On a DC 10 check, the PC can recall a major event that happened during the time period, or a famous person who lived during that time. For each 5 points above the DC, he can recall another piece of information.
On a DC 10+, check, he can recall specific information – for example, who fought in the Battle of Fallon's Crossing 350 years ago. The DC is increased by how long ago the event occurred or the person lived (+5 per hundred years is a good rule here), and how obscure it was – recalling the events or name of a major battle would be +2 to +4, while trying to name the leader of an obscure adventuring company would be +10 to +15 or more.