Complex sentence: In the southwest were opium trails from Yunnan and Guizhou that ran through Baise and then down the river to Nanning, from there opium usually went out through Wuzhou, where the trade was financed.
Split into simpler sentences: In the southwest there were opium trails from Yunnan and Guizhou that ran through Baise and then down the river to Nanning. From these opium usually went out through Wuzhou, where the trade was financed.