The territory that now constitutes Tajikistan was previously home to several ancient cultures, including the city of Sarazm of the Neolithic and the Bronze Age, and was later home to kingdoms ruled by people of different faiths and cultures, including the Oxus civilization, Andronovo culture, Buddhism, Nestorian Christianity, Zoroastrianism, and Manichaeism. In what year did Tajikistan become a dependent nation?