im not sure
BUT
In 1227 the Mongol dominions stretched over the vast regions between the Caspian and China seas, bordering in the north on the sparsely populated forest belt of Siberia and in the south on the Pamirs, Tibet, and the central plains of China. This empire contained a multitude of different peoples, religions, and civilizations, and it is only natural to seek the motivating force behind this unparalleled expansion.
so its probably caspia