In the book gone with the wind how does rhett make money during the war?

The info. below leads me to believe that he was a shipping magnate.

George Trenholm as historical basis for Rhett Butler
It made international news in 1989 when Dr. E. Lee Spence, an underwater archaeologist and shipwreck expert from Charleston, South Carolina, announced his discovery that Margaret Mitchell had actually taken much of her compelling story of love, greed and war from real life and that Mitchell had actually based most of Rhett Butler on the life of George Alfred Trenholm. Like Rhett, Trenholm was a tall, handsome, shipping magnate from Charleston, South Carolina, and made millions of dollars from blockade running. Both the real life Trenholm and the fictional Rhett were accused of making off with much of the Confederate treasury and were thrown in prison after the Civil War where they were visited by a beautiful woman with a "fast" reputation. Spence's literary discovery that had its roots in his prior discoveries of some of Trenholm's wrecked blockade runners made international news.

In his book, Treasures of the Confederate Coast: The "Real Rhett Butler" and Other Revelations, Dr. Spence reveals what the editors of Life magazine called "overwhelming evidence" that shipping and banking magnate George Trenholm was the historical basis for Mitchell's romantic sea captain.