Answer:
i think it is D) moving people easier and cheape
The main reason was the South wanted to preserve slavery. The North wanted to abolish it. If you want some other reasons than slavery, let me know, and I will do my best to add more to this answer.
The international attitude was the world wanted revenge through a peace treaty and holding Germany accountable for all the damages.
It killed almost 50% of the population. They were devastated. Because there was no cure for it, they turned their faith towards God.
