Two issues: The desire to "unite the Germanies" - at least amidst Germanic peoples - may be dated to the late eighteenth/early nineteenth century, and in the early nineteenth was partly in resistance to Napoleon's defeat and humbling of Prussia and Saxony in 1806 (ironically, in forming the Confederation of the Rhine out of numerous minor dukedoms and principalities, Boney gave an impetus and a modern state structure to the unification interest). The resistance to French domination involved, among other things, the liberal, elite developing an interest in national traditions, "Volkslied"/folksong and the like. Of course, such cultural interest was used by the ruling class as part of an imperialist policy in the later nineteenth century; but then, "jingoism" wasn't exactly confined to them. Wasn't it Haydn who wrote the music of "The Emperor Hymn", i.e. that to which "Deutschland U. A." was added? Notice that some C of E hymn or other has this tune; as Brendan Behan said, it just reminds you where the Brit Royal Family comes from, and that they all speak German among themselves anyway.