Identify the motivations for German foreign policy as directed by Bismarck in the years after the Franco-Prussian War (War of 1870). How did they contrast with the later German drift toward war in the early twentieth century?

It was precisely Prussia's victory in the Franco–Prussia War that created Germany. After the war, Prussia united several German states into a single empire they called the Second Reich. The architect of this unification was Otto von Bismarck, the Chancellor of Prussia.
The creation of Germany upset the balance of power in Europe. However, the wealthy, industrial nation was not aggressive. On the contrary, Germany advocated for peace in order to avoid any war that threatened the existence of the new empire. Bismarck focused on two main threats: France and the Balkans.
France wanted revenge after its defeat in the Franco-Prussian War, so Bismarck isolated it to prevent the formation of any new alliances. In the Balkans, the Ottoman Turks were losing control, and Russia and Austria-Hungary hoped to gain power in the region. The threat of a war over the Balkans was very real, and it was a war Germany could easily have been drawn in to due to its ties with Austria-Hungary. To avoid this, Bismarck orchestrates negotiations, alliances, and mediations. The first major agreement formed by Bismarck was the Three Emperor's League which allied Germany, Russia, and Austria-Hungary.
However, tensions in Europe continued to rise, and the German government wanted to stay one step ahead. In contrast to the previous peace-keeping foreign policy, Bismarck formed a military alliance between Germany and Austria-Hungary stating each country would come to the defense of the other if France were to attack. Italy later joined this agreement, creating the Triple Alliance.
When Kaiser Wilhelm II came to power in Germany, he resented Bismarck's power and influence and fired him. The Kaiser abandoned Germany's role as the neutral mediator of Europe and focused on Germany's relationship with Austria-Hungary, letting all other agreements expire. When several ethnic groups within the Austro-Hungarian Empire began to push for autonomy or independence, Germany sought to preserve the empire, as it was their only powerful ally. Conflicts worsened, and Germany pledged support to Austria-Hungary in the invasion of Serbia. This pulled Germany into the First World War, during which it installed the very aggressive Schlieffen Plan, a very swift invasion of France via Belgium.