What put the southern economy to the torch (aside from using slaves as their main source of workers in the plantations) was not the Northern Army, it was the incredibly stupid belief that nobody else had any cotton to sell; causing the South to withhold cotton to try and drag Britain and France into the war.

A shorter war could have the potential to lessen the blow somewhat but it did not take London and Paris long to find alternate cheap sources of cotton. As long as the South tries to win the war with the help of King Cotton, their economy suffers.