The correct answer is because Otto Von Bismarck spent a lot of money to build up a strong Prussian army.
Otto von Bismarck(1815-1898), known as the “Iron Chancellor”, unified the nation and Germany became a modern state. Otto Von Bismarck spent a lot of money to build up a strong Prussian army that allowed him to lead Prussia and then, Germany after the unification.
Due to its great army, Bismarck declared war with Denmark, Austria, and France in order to unite 39 independent German states under Prussian control.
The origins of the Royal Prussian Army can be traced as far back as the mercenary forces of Brandenburg during the war from 1618 to 1648. King Frederick William I of Prussia made it bigger