It sounds like you are talking about the Lusitania. Is that correct?
It was "nationalism" that replaced the feelings of sectionalism in the early 1800s, since this was a time of great physical and emotional growth for the US, in which the country started to feel more like a single "unit".
The U.S. entered World War I because Germany embarked on a deadly gamble. Germany sank many American merchant ships around the British Isles which prompted the American entry into the war.
Answer:
southern states economys were almost totally dependent on slavery while border states had some industrialization
Explanation: