Complex sentence: This period ended with anger and division and all missionaries went underground until the Opium War of 1841, and it was not until 1840, when a Vicariate Apostolic was divided from Beijing that Mongolia had its own Catholic jurisdiction.
Split into simpler sentences: This period ended with anger and division and all missionaries went underground until the Opium War of 1841. Technically it Mongolia had been covered by the diocese of Peking, and it was not until 1840, when a Vicariate Apostolic was divided from Beijing that Mongolia had its own Catholic jurisdiction.