During the international political unrest caused by the American Civil War, Force was sent to Europe by the Lincoln Administration to stabilize diplomatic relations with France and England.

[7] Force began his varied career as a journeyman printer working for William A. Davis in New York City, and performed so well he was soon made the director of the office at age sixteen.

[2] Four years after arriving in Washington he founded and published an annual devoted to recording the facts of early American history, with its wide scope of official and statistical information.

[17] During his lifetime he was also a member of the Smithsonian Institution and the United States Naval Observatory, and played a major role in organizing the American Historical Society, in Washington in 1836.

[19][3][4] In November 1861, Force was sent to Europe at the recommendation of influential friends in President Lincoln's administration in a diplomatic effort to appeal to the political circles in Paris and London concerning their precarious relations with the Union and the Confederacy.

Force was accompanied by Archbishop Hughes and Bishop McIlvaine with the hopes of inducing the respective governments to refrain from giving aid to the Confederacy.

On June 9 of that year the Typographical Society expressed their gratitude for Force's safe arrival from a mission "fraught with the safety, honor and welfare of our country," and invited him to visit its chambers so that his fellow-members could express their thanks and congratulations for his diplomatic efforts in convincing the governments and people of Europe of the Union Government's ability to defeat the Confederacy.

[20] During the American Civil War, Peter's son, Manning Force rose through successive ranks to become a major-general in the Militia of the District of Columbia.

[21][6][15] During the Northern Virginia campaign of 1862 General Robert E. Lee and his army were getting dangerously close to Washington D.C.[22] Charles B. Norton, a Union colonel on the staff of General Fitz John Porter was, in civilian life, also an archivist and publisher, and offered to hide and store Force's large library of Americana over the concern of a possible Confederate attack on the capitol, but Force declined his offer.

He published Tracts and Other Papers, Relating Principally to the Origin, Settlement, and Progress of the Colonies in North America (4 vol Washington, 1836–1846), which comprised rare pamphlets.

It extended to nine volumes, which had been carefully arranged with great care and consummate skill, but after the delivery of the ninth volume the officials upon whom the law imposed the necessity of giving a viable review never managed to read the manuscripts, and the prospective publication of the work came to a standstill while Force was still eager to continue, and had many important documents and manuscripts yet to be printed.

Futilely Force continued his efforts to prevail upon complacent and uninterested officers to reverse the action of their predecessors, and finally, and reluctantly, relinquished his cherished project, which he had earnestly pursued for more than 30 years.

Force traveled about the eastern seaboard of the United States "ransacking" the book-shops and attending book auctions from Boston to Charleston in his tireless search for rare volumes.

Into his elder years Force often visited the War Department, approaching various Army officers he knew in his quest for archival material.

Because of its enormous size, totaling approximately 150,000 items, it was necessary for the committee to enter closely into details, and to devote much time and assiduous effort to the task of assessing Force's library.

The committee spent at least two to three hours per day, for a two month period, in the examination of every document, manuscript, book, map, etc, that passed through their hands.

[4] It wasn't until the late twentieth century was the value of Force's collection of documents, manuscripts, books and other archival material finally recognized by much of the historical community.

Force's vast collection of archives possessed the only surviving copies of many important documents of the colonial and revolutionary eras and proved to be a valuable scholarly resource.

Many large research libraries in the United States and around the world hold Force's nine volume published works in their collections, however, it remains a relatively underused source of information.

Scholars, historians, and students alike have found the massive work difficult to navigate using Force's complicated and varied index for the wide assortment of materials.

[33] Force maintained his ardent pursuit of collecting books, newspapers, manuscripts and other documents up until the week before he died, on January 23, 1868, at the age of 77.

[34] He is buried alongside his wife in Rock Creek Cemetery in Washington D.C. Force's grave marker was designed by German sculptor Jacques Jouvenal.