Complex sentence: This last breach of diplomatic immunity led to the 1868 Expedition to Abyssinia under Robert Napier, who came from India, the then colony of the British, with more than 30,000 personnel which consisted of not only soldiers but also other personnels such as engineers.
Split into simpler sentences: This last breach of diplomatic immunity was the catalyst to Britain launching the 1868 Expedition to Abyssinia under Robert Napier. He traveled from India, then a British colony, with more than 30,000 personnel, who consisted of not only soldiers but also specialists such as engineers.