Complex sentence: Thus Karl Marx's father became a "New Protestant" lawyer and a Prussian local politician who had converted from Judaism, something favoured during the Napoleonic Wars (before 1815) not only by Napoleon I but also by King Frederick William III of Prussia.
Split into simpler sentences: Thus Karl Marx's father became a "New Protestant" lawyer and a Prussian local politician. He had converted from Judaism, something favoured during the Napoleonic Wars (before 1815) not only by Napoleon I but also by King Frederick William III of Prussia.