After its crushing defeat of France in 1870, the newly united nation of Germany became the most important European power. It's long rival France, was now smaller, weaker and less economically dynamic and was not only beaten but profoundly isolated due to the long enmity with Britain and Russia, and Bismark made it his business to keep France weak and isolated. The other power, the Austro Hungarian Empire, was ally.
Kaiser Wilhelm II fired Bismark, and made Alfred Tirpitz head of his navy. Together they embarked on an ambitious ship building program designed to be able to confront Britain on the high seas. This, together with some other slights and rivalries deeply angered the British, who countered with their own ship building program. Meanwhile, the Kaiser's new Chancellor let the old treaty with Russia expire.
France exploited the moment to settle its differences with both Russia and Britain, forming the so-called Entente Cordial.
[British Prime Minister] Lloyd George recalled in his war memoirs that he went to visit the Liberal elder statesman Lord Rosebery on the day the Entente was announced. “His first greeting to me was: ‘Well, I suppose you are just as pleased as the rest of them with this French agreement?’ I assured him that I was delighted that our snarling and scratching relations with France had come to an end at last. He replied: ‘You are all wrong. It means war with Germany in the end!’ ”
Macmillan, Margaret (2013-10-29). The War That Ended Peace: The Road to 1914 (Kindle Locations 3398-3402). Random House Publishing Group. Kindle Edition.