They did make sure of it, in the sense that there were 44 years of peace between both countries.

In 1870, Germany had diplomatically isolated France: it was on very friendly terms with Russia, Austria-Hungary (League of the Three Emperors), Italy, and the UK; it encouraged the formation of the French colonial empire, thus diverting French energies away from Europe, and into possible conflict with British interests as well (Fashoda). In addition, Bismarck was initially opposed to the annexion of Alsace-Lorraine into the German empire, because it would generate constant French revanchism.

In the next decades, basically all of these changed, most crucially after Bismarck's 1891 dismissal. By then Germany had allied closely with Austria-Hungary, whose interests in the Balkan were by then opposed to the Russians, so Germany did not renew their Russian alliance. In addition, the Kaiser wanted to be a “modern” great power, which meant colonies and Weltpolitik, which meant a huge, modern navy, which meant conflict with the UK - just at the time when the UK and France had solved their differences (France now being the number-two Continental power and therefore natural ally of the British).