Complex sentence: Hart's calmness and good judgement in the face of conflict between the Chinese and Portuguese earned him favourable recommendations from his superiors and led to his nomination, in March 1858, as secretary to the Allied Commissioners governing Canton.
Split into simpler sentences: Hart's calmness and good judgement in the face of conflict between the Chinese and Portuguese earned him favourable recommendations. In March 1858, as secretary to the Allied Commissioners governing Canton.