Complex sentence: During December 1878 they left New York in order to move the headquarters of the Society to India, where it later was established at Adyar, as Theosophical Society Adyar.
Split into simpler sentences: During December 1878 they left New York in order to move the headquarters of the Society to India. The headquarters of the society were established at Adyar, as the Theosophical Society Adyar.