Complex sentence: The introduction of the Viscount roughly coincided with the opening of a major airport at Salisbury, the Viscount became the mainstay of the route between Johanesburg in South Africa, Salisbury (now renamed Harare) in modern-day Zimbabwe, and London, England.
Split into simpler sentences: The introduction of the Viscount roughly coincided with the opening of a major airport at Salisbury. The Viscount became the mainstay of the route between Johanesburg in South Africa, Salisbury (now renamed Harare) in modern-day Zimbabwe, and London, England.