During his tenure, the nation and Congress were in tremendous political upheaval over slavery, that included violence, disorder, and disturbances of the peace. In 1856, pro-slavery advocates invaded Kansas and used violent tactics against those who were anti-slavery. In May 1856, Senator Charles Sumner was viciously attacked by Preston Brooks in the Senate Chamber. At the expiration of his term, he traveled with his family to Europe and remained there until shortly before the opening of the American Civil War, when he returned to begin actively campaigning for the election of Abraham Lincoln. While in France, Fish studied foreign policy with diplomats and distinguished Americans; having gained valuable experience that would eventually benefit his tenure as Secretary of State.