All of these stereotypes contributed to the coming of the war by highlighting the tensions that already existed between Northerners and Southerners. The actions of people like John Brown were seen as extreme, and were taken badly by the South. The South began to believe that Northerners were serious about destroying their institutions, which made them more defensive.
In the case of Uncle Tom's Cabin, the depiction of slavery was very controversial. On the one hand, Southerners believed that slavery was depicted in very negative and cruel terms which did not reflect reality. On the other hand, many Northerners were shocked to find out about this problem in detail, which allowed the abolitionist movement to gain more force, and the problems between North and South to increase.