The correct response is: "The number of slaves in Texas increased in the years before the Civil War."
Prior to the Civil War, slavery became a significant part of Texas's economy, particularly as the demand for cotton increased. While not all white Texans owned slaves, the overall number of enslaved individuals in Texas rose notably leading up to the Civil War. After the abolition of slavery, former slaves did not immediately enjoy full citizenship rights; it took many years and significant legal changes for these rights to be recognized fully.