Complex sentence: His rule as a monarch had at times been marked by indecisiveness and inaction, and his ending years marked by hostility between himself and his elder son; nonetheless, it is to his credit that he left his kingdom in condition better than he had found it.
Split into simpler sentences: His rule as a monarch had at times been marked by indecisiveness and inaction, and his final years were marked by hostility between himself and his elder son. Nonetheless, it is to his credit that he left his kingdom in a better condition than he had found it.