But he was also interested in modern literature and philosophy; and the troubles of the times, of which he had personal experience, aroused in him a strong feeling of German patriotism, though throughout his life he was always proud of his connection with Scandinavia, and Gustavus Adolphus was his particular hero.
In this capacity he began, by means of memoirs or of articles in the Kieler Blätter, which he founded himself, to appear as an able and zealous champion of the half-forgotten rights of the Elbe duchies, as against Denmark, and of their close connexion with Germany.
It was he upon whom the Danes afterwards threw the blame of having invented the Schleswig-Holstein question; certainly his activities form an important link in the chain of events which eventually led to the solution of 1864.
Whereas at that time mere speculation dominated both the French Liberalism of the school of Rotteck, and Karl Ludwig von Haller's Romanticist doctrine of the Christian state, Dahlmann took as his premises the circumstances as he found them, and evolved the new out of the old by a quiet process of development.
Though deprived of his position and banished, he had the satisfaction of knowing that German national feeling received a boost from his courageous action, while public subscriptions saved him from poverty.
His Politik (1835) had already made him a name as a writer; he now published his Dänische Geschichte (1840–1843), a historical work of the first rank; and this was soon followed by histories of the English and French revolutions, which, though of less scientific value, exercised a decisive influence upon public opinion by their open advocacy of the system of constitutional monarchy.
Though no orator, and in spite of a personality not particularly amiable or winning, he produced a profound impression upon young men by the pregnancy of his expression, a consistent logical method of thought based on Immanuel Kant and by the manliness of his character.
[1] He remained one of the chief promoters of the well-known conference of the imperial party at Gotha, the proceedings of which were not, however, satisfactory to him; and he took part in the sessions of the first Prussian chamber (1849–1850) and of the parliament of Erfurt (1850).
But finally, convinced that for the moment all efforts towards the unity of Germany were unavailing, he retired from political life, though often pressed to stand for election, and again took up his work of teaching at Bonn.