At the same time he studied the history of the Thirty Years' War, and in 1835 (in Stuttgart) published "Gustav Adolf, König der Schweden und seine Zeit" (4th ed., 1863), in which by emphasizing the political role of the Swedish king he took a position diametrically opposed to the views previously held by Protestants. An equally profound impression, especially in Catholic circles, was produced by his "Allgemeine Kirchengeschichte" (4 vols., Stuttgart, 1841–46). Closing with the year 1305, it emphasises the part played by the Catholic Church in the development of the German Empire, and extols the policy of the popes. Shortly afterwards he was appointed professor of history at the Catholic University of Freiburg (Breisgau) -- an appointment which at first sight appears surprising, inasmuch as he was a rationalist, the results of those investigations were not at all times in harmony with Christian doctrine. His call, however, is quite intelligible in view of the tendencies of his recent writings, and of his fair treatment of religious questions, which seemed to indicate a gradual return to more conservative religious opinions. In 1848, he was elected to the German Parliament at Frankfurt as representative of a district of Württemberg; he belonged to the greater German party, and was a fanatical opponent of Prussia. It is a notable fact that, while in Parliament, he proposed a motion for the reunion of Catholics and Protestants, but only on condition that the Holy See would promise never to permit the Jesuits or Redemptorists to settle on German soil. In 1853 he entered the Catholic Church, after all the other members of his family had taken the same step. His later publications are: "Geschichte der ost- und westfränkischen Karolinger" (Freiburg, 1848, 2 vols.); "Die Urgeschichte des menschlichen Geschlechts" (Schaffhausen, 1855, 2 vols., incomplete), a demonstration that neither critical history nor the natural sciences, in treating of the origin and earliest history of the human race, can lay claim to certainty, when opposed to the earliest traditions of mankind and especially to Holy Writ; "Papst Gregorius VIII and sein Zeitalter" (Schaffhausen, 1859–61, in 7 vols.), a part of his "Church History", notable for its brilliant scholarship and conscientious research.