Pathfinder in the Grand Duchy of Karameikos
Background Information on Mystara on Youtube
There are a bunch of good little videos on Mystara if you want to get a feeling for the campaign wold. I am posting links to some of the more pertinent ones below.
But there are several others on other countries as well and other elements of the world. This campaign may not follow history, current events, or future events exactly as given in the videos, but this is an easy way to get some immersion into the game world overall.