Otto von Bismarck pushed Germany to unification mostly because he wanted power. He wanted to be the new and German Napoleon. In order to do that, he believed that he should have a unified country rather than a bunch of states with no unification or recognition of each other whatsoever.
His method of achieving this unified Germany consisted of using nationalism in order for Prussian conservatives to outmaneuver them. He also pushed it through “Blood and Iron” (speech that claims that a strong industry and military was needed in a country for success) as well as strong enforcement and comprehension of realpolitik.
Earlier attempts failed because there was no focus on unifying he country as a whole, and the different political groups on the German territory never seemed to agree on how to unify and they also didn’t count on a ruler as influential or demanding as von Bismarck.
After its formation, the German Empire became a huge industrial and military power. They had gotten so successful, they had already surpassed France, Russia, Austria-Hungary, and they were close to beating the British Empire.
This caused tension between the nations to increase, and soon, military alliances would form between the countries, the Austro-German alliance and Franco-Russian alliance being among them.
These conflicts would eventually play a big role in picking sides on the future Great War, alias World War I.