From Wikipedia

 The Boer War

 The Second Boer War was a major turning point in British history, due to world reaction over the anti-insurgency tactics the British army used in the region. This led to a change in approach to foreign policy from the UK who now set about looking for more allies. To this end, the 1902 treaty with Japan in particular was a sign that the UK feared attack on its Far Eastern empire and saw this alliance as an opportunity to strengthen its stance in the Far East. This war led to a change from "splendid isolation" policy to a policy that involved looking for allies and improving world relations. Later treaties with France ("Entente cordiale") and Russia, caused partially by the controversy surrounding the Boer War, were major factors in dictating how the battle lines were drawn during World War One.