There are not many English words shorter than or - 2, to be precise. But being short is no guarantee of being unambiguous, as the following sentences will show.
What does or mean here?
This is the common and easy use of or. You can have tea or you can have coffee.
This could be a request from the art teacher, but does it mean: You must colour the sea either all green or all blue? Or does it mean: You may use blue and green for the sea, in any combination of the two colours? There is no way of knowing.
In this case or does not mean that slaves fought either in the American Revolution or in the War of Independence. Nor, of course, does it mean that they fought in both of these periods. Or is used to introduce an alternative term for American Revolution.
This might not seem particularly difficult, but put yourself in the position of being an ESL student reading these homework instructions: