Complex sentence: McKinsey generally followed the Harvard school of thought that the company should use external consultants for its non-core activities (compare the management style of Warwick Fairfax, FXJ, between 1987 and 1990).
Split into simpler sentences: McKinsey generally followed the Harvard school of thought, that the company should use external consultants for its non-core activities. Compare the management style of Warwick Fairfax (FXJ between 1987 and 1990).