“You people of the South don't know what you are doing. This country will be drenched in blood, and God only knows how it will end. It is all folly, madness, a crime against civilization! You people speak so lightly of war; you don't know what you're talking about.
War is a terrible thing! You mistake, too, the people of the North. They are a peaceable people but an earnest people, and they will fight, too. They are not going to let this country be destroyed without a mighty effort to save it … Besides, where are your men and appliances of war to contend against them? The North can make a steam engine, locomotive, or railway car; hardly a yard of cloth or pair of shoes can you make. You are rushing into war with one of the most powerful, ingeniously mechanical, and determined people on Earth — right at your doors.
You are bound to fail. Only in your spirit and determination are you prepared for war. In all else you are totally unprepared, with a bad cause to start with. At first you will make headway, but as your limited resources begin to fail, shut out from the markets of Europe as you will be, your cause will begin to wane. If your people will but stop and think, they must see in the end that you will surely fail.”
A prescient quote from William Tecumseh Sherman
In the first part of the war the South had better generals, namely Robert E Lee and Stonewall Jackson, and they won a number of victories. But as time went by, the greater resources of the North began to tell and Lincoln got much better leadership in the form of Grant and Sherman. After that, the defeat of the South was probably a foregone conclusion.
At the end, Robert E Lee refused to countenance a guerilla resistance. He was an honorable man and thought such a thing not only dishonorable, but bad for everyone. I'd say he was right.
