The city's economy and its writers, painters, architects, and philosophers all made Florence a model of Renaissance culture.
"The South had more immigrants in large cities" was not a reason for the growing division between North and South after 1820, since the North had far more immigrants.
Because it involved countries all over the world, there was new technology such as chemical warfare, tanks, planes, etc. and it was unrestricted warfare. The countries were attacking civilians as well. Also there were diseases.
