President Lincoln suspended the writ of habeas corpus in an effort to protect public safety and reduce the potential for rebellion. There were many people in Maryland who were sympathetic to the Confederate army. Maryland was strategically important because all of the overland supply and communication lines ran through Baltimore.
President Abraham Lincoln issued his order to General Winfield Scott on April 27, 1861 as a means to protect vulnerable rail lines. Maryland's loyalties to the Federal Government were uncertain, and the President ordered the arrest of several members of the Maryland legislature who had Confederate sympathies.
John Merryman, of Cockeysville, Maryland was arrested for recruiting and training Confederate soldiers. John Merryman's attorney petitioned the federal court for a writ of habeas corpus, and the writ was granted by Chief Justice Roger Brooke Taney. His order to appear before the court was ignored by the military officers that were holding John Merryman prisoner. Chief Justice Taney found the suspension unconstitutional when he issued his opinion, asserting that only Congress had the authority to suspend the writ of habeas corpus. President Lincoln's proclamation on Sept. 24, 1862 expanded his earlier order of suspension to include every state in the country, and allowed the arrest of anyone who was critical of the Union war effort, including newspaper editors. In addition to protecting strategically sensitive areas, the suspension of the writ also allowed the government to try people in a military court.