Question

How did Bismarck use war to create a united Germany under Prussian rule?

Answer 1

Chancellor Otto von Bismarck was savvy enough to know that the divided German states would rally together around a united cause if they fought in war together for a common cause.  So Bismarck provoked a number of wars -- always making it look like he and Prussia were defending German national interests, not acting as the primary aggressors.  He strategically sparked war with Denmark over territories that were more German than Danish and thus (Germans felt) should not be under Danish control.  On the heels of that issue, he lured Austria into a war that enabled Prussia to establish itself as Austria's equal.  Finally, he provoked the French into declaring war on Prussia.  (Look up a little thing called the Ems Telegram if you want to know how that happened.)  The end result was the defeat of France and the declaration of a German Empire (the Second Reich, as it became known.)