The Jefferson-Lehman Treaty: The Relationship of Thomas Jefferson and James Lehman in the Exclusion of Slavery from Illinois and the Northern Territory, with Related Documents 1781-1818 is a historical book written by author Willard Cary McNall. This work explores the important topic of the struggle for the abolition of slavery in the northwestern region of the United States in the 18th and 19th centuries. The author details the interaction between Thomas Jefferson and James Lehman in this process, examining the written materials, joint efforts, and concerted actions of these prominent figures. The book is an important source for studying the history of the American antislavery movement and the development of political agreements aimed at banning slavery in the newly created territories. McNall's work expands our understanding of the key events and figures of the period, as well as perspectives on the moral and political aspects of the issue of slavery in America. The "Jefferson-Lehman Agreement" is an integral part of the history of the struggle for freedom and justice, as presented in McNall's scientifically based and detailed study.