Why was Otto von Bismarck considered as the chief architect of German unification

Why was Otto von Bismarck considered as the chief architect of German unification? Choose the correct option from the following :

1. He allianced with Italy and France for the unification process.
2. He granted autonomy to Prussia with Conservatives.
3. He carried the nation-building process with the army and the bureaucracy.
4. He carried Liberalist and Romantic scholars for cultural movement.

Answer: C

He carried the nation-building process with the army and the bureaucracy.