The answer is slavery. The Republicans were anti-slavery, while the democratic south was pro slavery. Eventually that, and a couple of other things, led to the Civil War.
Sorry if this was a bit late, Brainly had just recommended this question for me to answer, but I hope this helps!
He is referring to the bombing of Britain by Hitler's forces (also known as the Nazis). He was also said to have stated about this "It is not the size of the dog in the fight; but the size of the fight in the dog."
