Prussia was taken over and was considered the most powerful country in central Europe outside the Austro Hugnarian Empire.
First, from what I can tell, this game starts after the Napoleonic Wars.
Unification of nations, like Italy and Germany, would not necessarily be equivalent to wartime annexations. Most were annexed politically, and were not real annexations (most retained their own royal families within the empire, with the Prussian King being raised to German Emperor, allowing for other Kings to still retain their crowns).
Second, Prussia was never 'annexed' as what is being talked about here, but rather defeated in war, and forced to ally with France (until the tide turned).
Check out maps of the Napoleonic wars and you will see that France gained territories in the Belgian-Netherlands, North-Western Italy and the Dalmatian coastline. This was probalby the most extreme growth in the most recent timeframe (even though it does take place years before).
One of the issues I had with previous games is that you can claim just about any territory or nation without any true justification to the land. In this era of a game, nations only could gain territory that was justified through some historic, cultural or other means. You simply could not control an area that is hostile to your culture.
