Anglo-Russian Entente
From 1903 until his death in 1917, he was the Ambassador to the Court of St. James's, the chief Russian diplomat in the United Kingdom. His major achievement was to organize the signing of the Anglo-Russian Entente in 1907, which solidified relations between the two nations and helped create the Triple Entente, which, unlike the Triple Alliance or the Franco-Russian Alliance itself, was not an alliance of mutual defense. This broad diplomatic alignment would later form the Allied Powers of the First World War. He also formally proposed the agenda for the Second Hague Conference of 1907.