Why did Bismarck build a great army?

Bismarck built a great army to strengthen Prussia's position in Europe and to achieve his goal of German unification under Prussian leadership. He believed a powerful military was essential for asserting influence, deterring adversaries, and executing his diplomatic strategies, particularly in conflicts like the Austro-Prussian and Franco-Prussian Wars. This military strength enabled Bismarck to negotiate from a position of power and ultimately facilitate the unification of Germany in 1871.