The first Anglo-Japanese Alliance was signed in London on January 30, 1902 by Lord Lansdowne (British foreign secretary) and Hayashi Tadasu (Japanese minister in London). The alliance was renewed and extended in scope twice, in 1905 and 1911 before its demise in 1921. Briefly, the benefit to Britain was the establishment of an ally in East Asia who could help contain Russia and protect British commercial interests in China. For Japan, it was a necessary step in achieving recognition as a Power (if not a Great Power) and gave her the confidence to challenge Russia's occupation of Manchuria and designs on Korea. The Russo-Japanese War (1904-05) broke out about two years later in February 1904.
The alliance was renewed and strengthened in 1905 and 1911, but declined during World War One and finally expired in 1921, much to the regret of Sir Charles Eliot, and the pleasure of the United States and China.
References
Ian H. Nish, The Anglo-Japanese Alliance: The diplomacy of two island empires 1894-1907, The Athlone Press, London and Dover NH, first published 1966.
George Alexander Lensen, Korea and Manchuria between Russia and Japan 1895-1904: The Observations of Sir Ernest Satow (Sophia University, Tokyo and Diplomatic Press, Tallahassee, Florida, first published 1966)
See also