What was the historical significance of the Thirteenth Amendment?
The historical significance of the 13th Amendment is that it ended slavery in the United States.
From early colonial times until the end of the Civil War, slavery was legal in the United States (and in the colonies before independence). Not all states allowed slavery, but there was nothing in the Constitution that prevented it and many states allowed it. The Civil War was fought partly over the issue of whether slavery would continue to be legal.
The North, of course, won the Civil War. Having done so, it wanted to make sure the South could not rebuild the system it had had since that system had led to a civil war. Therefore, in December of 1865, the 13th Amendment was ratified and slavery was no longer legal in the US under the Constitution.