Professor Emeritus at the United States Naval Academy
This concept certainly involved a blockade, but it also involved an offensive movement along the axis of the Mississippi River, and a holding force in northern Virginia to keep the rebel armies tied down. In conformance with Lincoln’s hope that the seceding states would eventually come to appreciate the folly of their actions, and to gain time for the latent nationalism that Lincoln believed still existed in the South to assert itself, he hoped that these acts would isolate the South and compel the rebels to confront their dependence on the whole Union for economic health.
At this point in the war (April-May 1861) both Lincoln and Scott underestimated the emotional commitment of the secessionists to a war for independence. Though Lincoln did mount a blockade, and he did urge and support a Mississippi River campaign, he accepted fairly quickly that these actions alone would not bring the rebellious States back into the Union. This was evident as early as late May of 1861 when he urged Irvin McDowell to make an offensive movement toward Manassas in the campaign that resulted in the first Battle of Bull Run.
By then it had become clear that a blockade alone, no matter how impervious, would never reunify the nation. To be sure, the blockade did make an important contribution to the war--it limited imports into the Confederate States to less than a tenth of pre-war levels; it virtually stifled agricultural exports; and it cut the Confederacy off from the diplomatic support of potential allies--but by itself it could not be decisive. Even by 1864, with nearly 500 blockading ships on station, the blockade remained porous, and without the pressure of the land war, the South could have survived--even thrived--indefinitely. To reunify the nation, it took a long and bloody land war.