I was studying about the history of my discipline (literary studies) for a test and got sidetracked thinking about what I knew of the way other disciplines developed and realized I don't know much History's own history. I do know a modern historian approaches history from a different perspective than a historian in Ancient Greece would have. But how did we get from one way of thinking about history to the other?
Hi! You've touched on an incredibly important and very difficult issue in the study of history. Namely, that the way we study history has changed significantly over time, and the modern idea of critically examining the sources for bias is (unfortunately) very, very recent.
There's a huge amount of interesting stuff to get into, and in the interest of not re-treading any ground, here's a collection of excellent answers from past questions on your exact topic!
https://www.reddit.com/r/AskHistorians/wiki/theory#wiki_historiography_and_studying_primary_sources
To pick a few of the juicier ones, here's a piece on the modern handling of historical bias, by /u/mhbeals.
An example of older methods that you may have been exposed to before, namely 'Great Men History', popular around the 19th century, still influences many entry-level books and interpretations today. Needless to say, it's flawed, but useful in some ways.
Here's an excellent in-depth write-up on this concept, by /u/LordHussyPants.
Cheers.