"The Great North-western Conspiracy" is a historical account of an attempt by a group of Confederate sympathizers to establish a pro-Southern state in the northwestern United States during the Civil War. The book, written by I. Winslow Ayer, provides a detailed overview of the conspiracy, from its origins to its eventual downfall. The conspirators, led by a former Ohio congressman named Clement Vallandigham, sought to create a new state called "the Northwest Confederacy" out of the territories of Ohio, Indiana, and Illinois. They hoped to establish a base of operations from which they could launch attacks on Union forces in the East and ultimately win the war for the Confederacy. However, the conspiracy was uncovered by Union authorities and the leaders were arrested and tried for treason. Vallandigham was banished to the South but eventually returned to Ohio and continued to agitate against the Union cause. Ayer's book offers a comprehensive account of the conspiracy, including its planning, recruitment efforts, and failed attempts to gain support from foreign powers. It also sheds light on the political climate of the era and the deep divisions that existed within the country during the Civil War.