Simms was an internationally known author. He was a journalist and a historian. And he observed the destruction of Columbia first hand. He did lose something like 10,000 books [rb: from memory] in his library to theft and fire, both by the Union troops.
The huge fires that destroyed much of Columbia began at night started by Sherman's troops. They would rob a house of its valuable contents, then burn it. A few of Sherman’s sympathetic troops had earlier warned locals that this was coming. When local fire fighters attempted to put out fires, some of Sherman’s troops bayoneted and cut up the fire hoses.
Perhaps you would like some confirmation from sources other than Simms. How about 60 depositions? A commission was set up in 1866 by the state to document what happened. Depositions were taken from some 60 individuals. The results were quoted many years later by a 1920 history book: [Link: History of South Carolina]. Click on the link. It takes you to page 799 of the book. Read the bottom paragraph from page 799 through page 809, and you may come away with a different understanding of what went on. Page 808 and 809 deal with "The Burning Cotton Myth," which counters the source you cited.
Here is some more detailed information about the role, if any, that cotton had in the burning of Columbia in an 1866 book by Dr. Daniel Hayward Trevezant in the following link: [ The Burning of Columbia, S. C., A Review of Northern Assertions and Southern Facts ].
That link points out that fires started essentially simultaneously in widely scattered different parts of the city east, west and south of the central city.
On page 801 of the History of South Carolina book linked to above, Sherman is reported to have said the following in Salem, Illinois, in July 1865 about a change in policy he made on his march to the sea. "Therefore, I resolved in a moment to stop the game of guarding their cities and to destroy their cities."
Somewhere in my posts of years ago, I cited where Sherman acknowledged to the mayor and others that his (Sherman’s) troops burned the town.
Sherman gave testimony in an 1873 English-American commission about what happened to Columbia. The complete text of the commission proceedings were published in the New York Times. Here is some of Sherman’s testimony:
Q. -- You testified, a little while ago, that it was very likely they [Sherman's own men] might burn Columbia, and you permitted them, or your officers did -- permitted them to go about the town?
A. -- I could have had them stay in the ranks, but I would not have done it, under the circumstances, to save Columbia.
Q. -- Although you knew they were likely to burn Columbia, you would not restrain them to their ranks, even to save it?
A. -- No, Sir. I would not have done such harshness to my soldiers to save the whole town. They were men, and I was not going to treat them like slaves. ...
And here is some more of his testimony dealing with the plundering of the city by his troops.
Q. -- I understand you to say that you saw no pillaging going on along Richardson or Main-street during the hours of daylight on the 17th.
A. -- I did not.
Q. -- Not anywhere else in Columbia during the hours of daylight?
A. -- No, Sir.
Q. -- You were not apprised of it in any way?
A. -- I was not.
Q. -- You were not aware that almost every store along Main-street was broken into by men in Federal uniform?
A. -- I was informed by the Mayor that Wade Hampton's cavalry had gone through the town and plundered their stores before we got there; The Mayor himself reported that to me.
Q.-- I asked you if you are aware of that these stores were plundered by men in Federal uniforms subsequently?
A. -- I do not know anything about the Federal uniform being used by the rebels.
Q. -- I did not ask about the rebels; I asked a very simple question and I want an answer?
A. -- I heard nothing about the plundering of stores by our men during the day of our first occupation of Columbia.
Q. -- And know nothing of it?
A. -- I know nothing of it personally or officially.
Q. -- Do you know anything of it in any way whatsoever, individually, privately, or in any way?
A. -- No, Sir; on the contrary, there was very good order in the city; I walked about the streets like everybody else that day, and saw nothing out of the way; ...
Contrast that with Simms’ 1865 account in "A City Laid Waste":”
Hardly had the [Union] troops reached the head of Main street, when the work of pillage was begun. Stores were broken open in the presence of thousands within the first hour of their arrival. The contents, when too cumbersome for the plunderers, were cast into the streets. Gold and silver, jewels and liquors, were eagerly sought. No attempt was made to arrest the burglars. The officers, soldiers, all, seemed to consider it a matter of course. And wo to him who carried a watch with gold chain pendant; or who wore a choice hat, or overcoat, or boots, or shoes. He was stripped by ready experts in the twinkling of an eye. It is computed that, from first to last, twelve hundred watches were transferred from the pockets of their owners to those of the robbers. Purses shared the same fate; nor was Confederate currency repudiated.
Sherman's troops had marched into town in an orderly fashion. Then when they were dismissed, wholesale robbery and plunder began and lasted the rest of the day and night. From Simms again:
Sherman, at the head of his cavalry, traversed the streets everywhere – so did his officers – yet they saw nothing to rebuke or restrain. Subsequently, these officers were everywhere on foot, yet beheld nothing which required the imposition of authority. Robbery was going on at every corner – in every house – yet there was no censure, no punishment.
Here is Union Captain George Whitfield Pepper (who was there with Sherman's troops in Columbia) in his 1866 book:
Next morning [rb: the morning after the fire], in company with this same officer, I started to visit the ruins. On our way we met crowds of soldiers, "who were yelling, singing, waving gold watches, handfuls of gold, jewelry, and rebel shinplasters [rb: paper money] in the air, and boasting of having burned the town." One was staggering under the weight of a huge basket filled high with silver plate.
...
A number of Jews were standing by, weeping and exclaiming: "Me poor, me starb, starb, starb. Your mens come in mine house, kicks me out, sets fire to mine house. Me carry topacey out on the street. Your mens puts wood on him and purns all mine topacey." [rb: spelling and grammar as in Pepper's book].
Here from a letter by Union Lieutenant Thomas Myers wrote from Camden, S.C. after the burning of Columbia posted long ago by PeaRidge:
"My dear wife, we have had a glorious time in this State. Unrestricted license to burn and plunder was the order of the day. Gold watches, silver pitchers, cups, spoons, forks, etc are as common as blackberries. The terms of plunder are as follows: Each company is required to exhibit the results of its operations at any given place, -one-fifth and first choice falls to the share of the commander-in-chief and staff, one-fifth to the corps commanders and staff, one-fifth to field officers of regiments, and two-fifths to the company."
Believe whatever you want, Bull Snipe.
Correction: I listed “topacey” as a word the Jews were saying. When I looked at the word with a magnifying class, it was clear that the word was “topaccy”. The second “c” was not an “e” like I thought it was in the sometimes hard to read reprinting of the 1866 book’s text.