Well, Germany wasn't that unified in that the unification of Germany as such was only achieved by cutting ties with Austria, which traditionally had been a core part of Germany.

But there had been a strong desire for unity for decades. The Prussian king had been offered an imperial crown decades earlier but didn't want a crown that was offered to him by the common rabble - if he was to be emperor and unify the country, then it had to be under his terms in a top-down approach.