Complex sentence: The Concessions in Tianjin were concession territories ceded by the Chinese government to some European countries and Japan in Tianjin, then known as Tientsin (also spelled Tien-Tsin).
Split into simpler sentences: The Concessions in Tianjin were concession territories ceded by the Chinese government to some European countries and Japan within the city of Tianjin. At that time, Tianjin was also known as Tientsin (sometimes spelled Tien-Tsin).