The Cedar Swamp Historical Society's collection contains a letter from a Civil War soldier, Thomas S. Seabury to the Hon. John M. Williamson. Thomas Shepard Seabury (1829-1880) was a First Lieutenant of the 3rd New York Infantry on the Union side during the war. Stationed in Norfolk, Virginia, he was a signal officer who was responsible for communications between Union outposts. Seabury's mother, Ruth Hawkins Mount, was the sister of famous Long Island painter, William Sidney Mount. John M. Williamson (1787-1878) was a lawyer, politician and judge from Long Island. In his letter, Seabury refers to Williamson as an "old friend" with whom he shared "sage observations in times past" and "information concerning political affairs." Seabury writes to tell Williamson about the current situation that he sees unfolding from his position within the Army. He says that he thinks that Williamson will be interested in his opinion about the War and his belief that the outcome looks more likely to lead to "the destruction of a nation rather than ensure the reconstruction of a beneficent government."

Written on December 7, 1862, the letter details Seabury's feelings on the present situation of the Northern army and its changing of commanders. At the time the letter was written, President Abraham Lincoln had just removed General George McClellan from his position as commander of the Army of the Potomac. Lincoln was not pleased with McClellan's hesitancy to pursue the retreating Confederate Army when that action could have brought the conflict closer to its end. McClellan was replaced by General Ambrose E. Burnside. Seabury refers to this change in leadership in his letter and does not support it. He believes that radicals are pushing an agenda that led to the removal of McClellan and may lead to further changes. The radicals to whom he refers seem to be members of the government administration. It is not clear whether Seabury includes Lincoln in this group, however, since Lincoln was the person who removed McClellan from his leadership position, it is quite possible. Seabury sees the appointment of Burnside as a first step by the radicals and is concerned that their agenda will lead to further changes within the leadership of the military. He refers to the radical members of the administration as "visionary schemers" and fears that the natural habit of the Army to conform to discipline will give the administration more power to do as they wish. He also is concerned that the administration will accept the offer of armistice by the South which he believes will expose the divisions within the North concerning peace measures.

Seabury's letter provides a view of the Civil War through the eyes of a soldier. It shows that the Northern side was not completely unified and those who were in the military ranks did not necessarily agree with the decisions made by the political leaders.