Why was the slow Anaconda Plan adopted only later?

The short answer

• Geography as strategy. The Confederate defensive line could be crossed by water. The Tennessee and Cumberland gave Union vessels routes south, carrying supplies past roads made difficult by mud and bridges that defenders could burn. Northern yards converted river steamers into ironclad gunboats within months. With a tenth of the shipbuilding capacity, the Confederacy could not match them. The rivers mattered because Union foundries could put vessels on them; the foundries mattered because the rivers carried those vessels inland.
• The blockade’s slow arithmetic. Successful voyages were common: five in six runners got through in 1861, and one in two still did so in 1864. Yet each voyage had to bear the cost of risk. By 1863, a barrel of flour bought for $8 in Nassau reportedly sold for ten times as much in Charleston. The Confederacy needed cotton exports to pay for imports, and shipping the cotton had become harder too. A count of captures alone misses this pressure; prices and trade volumes show what continued passage cost.
• Grant emerges. Grant had failed at farming and sold firewood before returning to command. At Henry and Donelson he moved against the seam between two Confederate departments, where divided authority made a response harder, before his plan had been properly approved. His superiors continued trying to shelve him during 1862. Lincoln reportedly defended him: “I can’t spare this man. He fights.”
• Ironclads make the blockade possible. The battle at Hampton Roads (see the marker) showed what armor could do. The CSS Virginia exposed the vulnerability of wooden warships; the Monitor arrived that night and met her, and neither destroyed the other. The Union's advantage lay also in what came afterward. Its industry went on to outbuild the South in ironclads by an estimated twenty to one, making the new kind of ship available at scale.

What it changed

The Confederate heartland starts to bleed. Nashville and Memphis brought Southern iron and gunpowder mills and a productive farm belt within Union reach. The grey-tan wedge in Tennessee does not shrink again on the map. Confederate armies in the West would spend three years trying to recover ground opened by ten days of fighting in February.

New Orleans: the door closes from the sea. New Orleans fell without a land battle for the city. The Confederacy had lost its largest city and port, as well as its banking capital; the loss damaged the cotton trade that financed imports. The lower river's grey-tan band now reaches toward the Union position in the north, with Vicksburg still between them.

Contraband: emancipation from below. On the sea islands and in river towns, enslaved people reached Union forces and claimed freedom through their own actions. Officers called them “contraband of war” to avoid returning them. Their arrival forced practical decisions before the government had settled a national policy. Chapter 7 follows the political change.