Complex sentence: The government in turn backed the Niger expedition of 1841 (not including Buxton) put together by missionary organisations: it travelled to the Niger River Delta in 1841 and began negotiations, but suffered many deaths from disease, and cut short its mission.
Split into simpler sentences: The government in turn backed the Niger expedition of 1841 (not including Buxton) put together by missionary organizations. It began negotiations in the Niger Delta, but suffered many deaths from disease and cut short its mission.