Entering uncharted waters as he confronted the rebellion, Lincoln claimed broad emergency powers that he argued the Constitution had vested in the executive branch. Although he asserted powers as commander in chief that presidents had not before used, he did not create his war power out of whole cloth. Lincoln found the power he needed to deal with the rebellion in the commander-in-chief clause of the Constitution, in the clause of Section II requiring him to "take care that the laws be faithfully executed," and in his presidential oath "to preserve, protect, and defend the Constitution of the U.S."

Based on these powers, he called out the militia, authorized increases in the size of the regular army and navy, expended funds for military purchases, deployed military forces, blockaded Southern ports, suspended the writ of habeas corpus in certain areas, authorized arbitrary arrests, and empanelled military tribunals to try civilians in occupied or contested areas. Later he authorized conscription and issued the Emancipation Proclamation. Lincoln justified these steps as necessary to save the Union and preserve the Constitution.

Although Lincoln had no formal military education, he learned quickly and proved to be a competent strategist. He intuitively adhered to the old adage that in war, "the main thing is to make sure that the main thing remains the main thing." The "main thing" for Lincoln was to preserve the Union. But like any good strategist, Lincoln proved willing to adapt his strategy to the circumstances in order to achieve this goal.

Lincoln understood that the key to victory for the Union was the simultaneous application of military force at multiple points, making it difficult for the Confederacy to defend its territory. Although it was not successfully implemented until 1864, Lincoln articulated the principle early in 1862. He also understood that a successful strategy required Union armies to defeat Confederate armies, because they, not territory or the Confederate capital, constituted the Confederacy’s true "center of gravity."

Finally, he understood the importance of the West in Union strategy. In early 1862, Union armies had employed the Tennessee River as the "main line of operations" to penetrate deep into western Tennessee and northern Mississippi. Grant’s subsequent victory at Shiloh permitted Union forces to seize major parts of the Confederacy’s one remaining east-west railroad line and opened the way to both Vicksburg on the Mississippi River and Chattanooga. The capture of the latter permitted Union forces eventually to penetrate the Appalachian barrier and seize Atlanta.

Lincoln’s strategy also possessed a strong political element, which at the end of 1862 seized emancipation as its weapon. Emancipation struck not only at the war-making potential of the Confederacy but also at the heart of the Southern social system. But Lincoln had to tread carefully for domestic political reasons, because while emancipation was welcomed by abolitionists and their radical Republican allies in Congress, it was denounced by conservative Democrats in the North and loyal slaveholders in the slave states that remained in the Union. Lincoln needed both groups if he was to prosecute the war successfully, but in balancing their needs he was denounced by the conservatives as moving too fast and by the radicals as moving too slowly.

Lincoln was an activist commander in chief who frequently "interfered" with his generals. He intuitively understood that civilian leaders cannot simply leave the military to its own devices, because war is an iterative process involving the interplay of active wills. He realized that what appears to be the case at the outset of the war may change as the war continues, modifying the relationship between political goals and military means.

Perhaps the most important challenge Lincoln faced in the area of civil-military relations was that early in the war, his generals pursued the war they wanted to fight rather than the one their commander in chief wanted them to fight. This was particularly true in the case of Maj. Gen. George McClellan, who disagreed with many of Lincoln’s policies, and indeed may have attempted to sabotage them.

As war president, Lincoln saved the Union. It is hard to imagine that anyone else among his contemporaries could have done what he did. Many were willing to let the Union go to pieces. Many others would have pursued policies that lacked any element of consent. As Lincoln remarked on numerous occasions, public sentiment is critically important in a republic. In its absence, legislators cannot pass laws and presidents cannot execute them. Lincoln could have avoided war by making another of the base concessions that politicians had been making for several decades. But that would only have postponed the day of decision, making it unlikely that republican government could survive in North America or anywhere.

Lincoln’s war presidency teaches us that democratic institutions, as important as theymay be, by themselves do not save republics when they are threatened. It teaches us the necessity of prudence for successful democratic statesmanship, and that citizens of a democratic republic respond to strong, principled leadership in time of crisis.

Lincoln set a high standard for leadership in time of war. He determined the goals of the war, set the strategy, called forth the resources of the nation, appointed the agents of victory, took the necessary steps to restrain those who would cooperate with the disunionists, and provided the rhetoric that stirred the people. Yet he did these things within a constitutional framework. In the conflicts that confront us today, we face issues not entirely unlike those that confronted Lincoln, especially with regard to the issue of civil liberties in wartime.

The American Founders created institutions that have enabled the United States to minimize the inevitable tension between the necessities of war and the requirements of free government. The resultant ability of the United States to wage war while still preserving liberty is unprecedented. To his credit, Lincoln understood and took advantage of these institutions during the time of greatest stress on the American polity. In doing so, he established the precedents that have guided his successors in their attempt to keep the United States both safe and free.

Mackubin T. Owens is Professor of National Security Affairs at the United States NavalWar College.