The Triple Entente ("entente" — French for "understanding") was the alliance formed in 1907 among the United Kingdom of Great Britain and Ireland, the French Third Republic and the Russian Empire after the signing of the Anglo-Russian Entente. The UK already had the Entente Cordiale with France since 1904, while France had concluded the Franco-Russian Alliance in 1894.
Though not a military alliance, the alignment of the three powers, supplemented by various agreements with Japan, the United States and Spain, constituted a powerful counterweight to the "Triple Alliance" of Imperial Germany, Austria-Hungary and Italy, the latter having concluded an additional secret agreement with France effectively nullifying her alliance commitments.
Russia had been a member of the League of the Three Emperors with Austria-Hungary and Germany. After the League's collapse during the Alexander von Battenberg affair, German Chancellor Bismarck tried to keep an alliance with Russia. This was formalised in the Reinsurance Treaty of 1887. But when Bismarck was dismissed from office in 1890, Kaiser Wilhelm II failed to renew the treaty and Russia formed a military alliance with France. The UK had been asked to join in an alliance with Germany, but did not agree with Germany's ideological and military goals, and had been in a naval arms race with Germany for decades.
With the addition of Italy in 1915, the Triple Entente was the force that opposed the Central Powers during World War I. After the outbreak of World War I in Europe in August 1914, the three Entente powers undertook in September 4 not to conclude a separate peace with Germany or Austria-Hungary.
But Russia's separate armistice (December 1917) and peace Treaty of Brest-Litovsk on March 3, 1918, ended its alignment with the other Entente powers. The UK and France continued to collaborate in ultimately unsuccessful attempts to uphold the postwar order during the 1920s and 1930s, until France's crushing June 1940 defeat in renewed conflict with Germany forced her into a separate armistice, leaving the UK alone in Europe.
The Entente heralded the end of British neutrality in Europe. It was partly a response to growing German antagonism expressed in the creation of the Kaiserliche Marine battle fleet capable of threatening British naval supremacy.
Ironically, the Franco-Russian Alliance which had seemed weak during Russia's defeat in the Russo-Japanese War, later appeared the more powerful alignment, when Russia unexpectedly and rapidly recovered from the defeat and from the Russian Revolution of 1905, and when the UK was added as a diplomatic partner. This contributed to the foreign-policy adventuring and contemplation of pre-emptive war, which culminated in German readiness for conflict in 1914.