If you want a quick, simple guide to German history, you could give the following animations a try, which quickly although simplistically gives you an idea of the origins of German history up to the present day (in 5 minutes…)!
To get an idea of how complex the patchwork of German states were on the eve of the Napoleonic wars, you could look at the map. Every colour represents a different state:
Much more in depth….
The Art of Germany
The background to German unification is the emergence of nationalism – mainly as a romantic ideal that emerged from the ashes of years of German defeat from the French and before them, the Swedes.
https://dailymotion.com/video/x6e9ymr Schubert’s Eolkonig – an illustration of Romantic themes Worth watching with subtitles switched on to ‘English’.
Background to Prussia – short but deep history!
Really detailed but excellent on medieval background