Although Frankfurt am Main, one of the four "free cities" in the German Confederation, had remained neutral during the recent Austria-Prussia War, Prussia had annexed the area by proclamation backed with the threat of force on September 20, 1866. Two and a half weeks later, Prussian officials took formal possession of the city along with its 90,000 inhabitants and incorporated them into the Prussian state of Hesse-Nassau. (By John Osborne)
Source Citation
"Frankfort," The American Cyclopedia and Register of Important Events of the Year 1866 (New York: D. Appleton and Company, 1873), 336.