Bactria was a province of the Persian empire located in modern Afghanistan, Uzbekistan, and Tajikistan.
After the defeat of Darius III of Persia, Bactria continued to offer resistance against Alexander the Great, led by Bessus, who had proclaimed himself successor to Darius. Alexander conquered it with great difficulty between 329-327 BCE, largely with the help of local auxiliary forces. During his stay there, Alexander married a Bactrian woman, Roxanne, to aid his effort of controlling the region.
After Alexander's death, Bactria was part of the Seleucid Empire. The many difficulties against which the Seleucid kings had to fight and the attacks of Ptolemy II of Egypt gave Diodotus, satrap of Bactria, the opportunity to declare independence (about 255 BCE) and conquer Sogdiana, founding the Indo-Greek Kingdom.
