Complex sentence: Napoleon's armies smashed armies of the Holy Roman Empire and then the social, administrative and legislative measures taken by Napoleon in the area smashed the feudal rule that the priests and the nobility had exercised over the area previously.
Split into simpler sentences: Napoleon's armies smashed armies of the Holy Roman Empire. His rule established social, administrative and legislative measures taken that broke up the feudal rule that the priests and the nobility had exercised over the area previously.