Several of Lincoln's loyal advisors, who were in a position to know the facts, reported to him in writing that the tariff, not slavery, was the cause of southern secession. These were explicit reports, clear and unambiguous, that need no subtle interpretation. They unanimously declared that southerners left because they wanted free trade.
Lincoln chose Stephen A. Hurlbut as his own secret emissary to Charleston, South Carolina. Although now an Illinois lawyer and Lincoln's political associate, Hurlbut had many contacts in Charleston. He was in a unique position to discover and advise Lincoln of political feelings there. His report to Lincoln just days before the war is excellent evidence of the reasons for secession.
Robert Hosea was a Cincinnati businessman and highly respected political figure with southern political, business and family contacts. His long letter to Lincoln is a wealth of information on the southern reasons for secession and their political maneuvering to get free trade.
Henry C. Carey was the country's leading political economist and Lincoln's principal advisor on political economy. He was an ardent tariff advocate. His letters to Lincoln in 1861 leave little doubt he believed the southern desire for free trade was the cause that had "broken up the Union."
Horace Greeley was the editor of the New York Tribune, the principal national political organ of the Republican Party. Greeley published in his newspaper an article giving the views of his secret Charleston correspondent on southern secession. It includes the report of an interview with a southern planter on his motivation for secession.
This highly credible evidence should become familiar to anyone interested in understanding the cause of the war. Students should know who these men were, what they said, how they came by their information and why Lincoln believed in them.
Historians who insist that the war was caused by slavery should be invited to debate Lincoln's advisors.