Final answer:
Bismarck rejected an alliance with Britain, focusing instead on the Dual Alliance with Austria-Hungary to counteract French and Russian threats, while Britain's traditional alignment with France and its 'splendid isolation' policy made an alliance with Germany less beneficial.
Step-by-step explanation:
Bismarck rejected a potential alliance with Britain in 1879 because his strategic focus was on maintaining a balance of power on the European continent, particularly to guard against threats from France and Russia. He engineered the Dual Alliance with Austria-Hungary to counter Russian influence and, by extension, a possible two-front war with France and Russia. An alliance with Britain was not seen as necessary at that time, particularly since Britain was traditionally more aligned with France and maintained a policy of 'splendid isolation' regarding European affairs. Moreover, his earlier manipulations, including inflaming Franco-German tensions and annexing territories after the Franco-Prussian War, were not conducive to British support. Thus, Bismarck prioritized alliances with central European powers to consolidate Germany's position and security.