Complex sentence: Her son Louis Napoléon, the future emperor Napoléon III, who had gone to school in Augsburg, also came to Arenenberg as a teenager; there he was further educated and from there went to attended the Swiss military academy at Thun and received Swiss citizenship.
Split into simpler sentences: Her son Louis Napoléon, the future emperor Napoléon III, who had gone to school in Augsburg, also came to Arenenberg as a teenager where he was further educated. From here he went to attended the Swiss military academy at Thun and received the Swiss citizenship.