The border was inherited from the old Persia-USSR border, which largely took its current shape during the 19th Century after the Russian conquest of Central Asia and its annexation of the Khanate of Kokand and the Emirate of Bukhara in 1865-68. In 1869 Persia and Russia agreed that the Atrek river would be the border between them. This boundary was confirmed and then extended eastwards to the vicinity of Ashgabat in 1881 following further Russian advances into Turkmen lands, and then to the border with Afghanistan in 1893; various further delimitations of this border occurred in the following years. Further small changes were made in the period 1954-57 when Iran and the USSR (as they now were) agreed to more clearly demarcate their common border, including the Atrek delta region which had since altered due to the shrinking of the Caspian Sea.