sentences:  It was only with the introduction of the Wilmot Proviso in August 1846 that the national debate began to split along sectional lines.During the "prolonged deadlock of 1846-50" the idea of secession as a possible solution to Northern threats against slavery began to take root among more and more Southerners.In December 1849 Congressman Alexander Stephens, the future vice-president of the Confederacy, wrote to his brother, "I find the feeling among the Southern members for a dissolution of the Union – if the antislavery [measures] should be pressed to extremity – is becoming more general than at first."