Complex sentence: In September 1805, the then Major-General Wellesley, newly returned from his campaigns in India and not yet particularly well-known to the public, reported to the office of the Secretary for War to request a new assignment.
Split into simpler sentences: In September 1805, Major-General Wellesley was newly returned from his campaigns in India and was not yet particularly well-known to the public. He reported to the office of the Secretary for War to request a new assignment.