Complex sentence: He then predicted that the slow-moving imperial troops would perform disastrously in the rough African terrain and, in spite of being a conservative imperialist himself, he was one of a large group of Cape MPs who implored Frere to rethink his policies.
Split into simpler sentences: He then predicted that the slow-moving imperial troops would perform disastrously in the rough African terrain. Altogether, in spite of being a conservative imperialist himself, he was one of a large group of Cape MPs who implored Frere to rethink his policies.