In 1867, President Andrew Johnson offered Bancroft the post of US minister to Prussia, enabling him to return to Germany. Bancroft remained in Berlin for seven years, and President Ulysses S. Grant appointed him minister to the German Empire in 1871. During his tenure in Berlin, Bancroft spent much time negotiating agreements with Prussia and the other north German states relating to naturalization and citizenship issues; they became known as the Bancroft Treaties in his honor. The treaties were the first international recognition of the right of expatriation. The principle has since incorporated in the law of nations.