It was called "The Anaconda Plan" after the slow-moving South American snake of the same name. Devised by the elderly and cranky General Winfield Scott, it was laughed at and worse by the northern press - until it worked. It consisted of a massive naval blockade of southern ports combined with army actions that sealed the Confederacy's western borders. It took time - which infuriated lots of northerners - but it did eventually contribute the most to the south's worsening inability to provide the basic necessities to it's troops and it's civilian populace.
Things were so bad for the Confederacy that when Robert E. Lee surrendered, he admitted most of his troops were starving, leading General Grant to order food from federal army stores to be given to the surrendering Rebs immediately. It was the first food most of them had had in days. This action went far in assuaging the sorrow and rage of the Confederate soldiers at having been defeated.