Complex sentence: The Enlightenment had gained great influence in certain Commonwealth circles during the reign (1764--95) of its last king, Stanisław August Poniatowski, and the King had proceeded with cautious reforms such as the establishment of fiscal and military ministries and a national customs tariff.
Split into simpler sentences: The Enlightenment had gained great influence in certain Commonwealth circles during the reign (1764--95) of its last king, Stanisław August Poniatowski. As a result, the King had proceeded with cautious reforms such as the establishment of fiscal and military ministries and a national customs tariff.