Throughout the 19th century Russia steadily advanced across Central Asia, conquering Tashkent in 1865, Samarkand and Kokand in 1868, and Khiva in 1873. Britain suggested Afghanistan as a buffer state, but following the June 1878 Congress of Berlin Russia sent a diplomatic mission to Kabul. Sher Ali Khan, the Amir of Afghanistan, attempted to keep the Russian envoys out, but they arrived in Kabul on 22 July 1878. On 14 August, the British demanded that Sher Ali accept a British mission as well. This incident resulted in the Second Anglo-Afghan War.