When South Carolina seceded from the Union in 1860, only ten of the other fourteen slave states followed. The legislatures of the remaining four—Maryland, Delaware, Kentucky, and Missouri—chose to remain in the Union. West Virginia eventually seceded from Virginia in 1861 and then in 1863 was admitted as a nonslave state in the Union.
To ensure the continued loyalty of these border states, Lincoln always had to maintain a moderate course in his policies. At times, he had to resort to force to prevent the border states from joining the Confederacy. In the spring of 1861, for example, Lincoln declared martial law in Maryland and sent troops to occupy the state after protesters attacked Union soldiers marching to Washington, D.C.
Had the border states seceded with the other slave states, the outcome of the Civil War might have been very different. First, the border states provided a geographical and ideological buffer between the combatants: had Maryland seceded, Washington, D.C., would have been entirely surrounded by Confederate territory. Second, the border states were important economic engines for the Union, primarily because Maryland and Delaware had so many factories. Had just those two states seceded, the Confederacy’s manufacturing capabilities would have nearly doubled. Because the Civil War was in many ways an economic war as much as a military one, doubling Southern manufacturing output could have seriously altered the duration and even the outcome of the war.
The fact that these slave states chose to remain in the Union also weakened the South’s claim that it had seceded to save its slavery-based economy. Nevertheless, Lincoln had to be careful not to offend slave owners in the border states, which is why, for example, the 1863 Emancipation Proclamation declared slaves free in only the secessionist states—not the loyal border states.
During the war, Lincoln faced opposition and criticism from a variety of groups in the North. Peace Democrats accused him of starting an unjust war on one side, while Radical Republicans in his own party accused him of being too soft on the Confederacy on the other.
In addition, many criticized Lincoln for using unconstitutional powers to achieve his goals. To prevent an insurrection in Maryland, he arrested several proslavery leaders in the state, suspended the writ of habeas corpus (which requires police to inform suspects of the charges against them), and imprisoned them until the war was over. Chief Justice of the Supreme Court Roger Taney ruled that the suspension was illegal and unconstitutional, but Lincoln ignored him, believing that his actions had been necessary to prevent further rebellion.