Two main issues that caused the civil war were slavery and the right to leave the union

There is often debate over the causes that lay at the start of the Civil War.  Some will say it was not primarily about slavery but about states' rights--their ability to do things their own way or even go their own way (leave the Union) if they wished.   The reality is that both issues lay at the heart of why the Civil War was fought.  A principal reason why the seceding states were asserting their rights and leaving was because of the issue of slavery.

John Pierce did a documentary study on "The Reasons for Secession," for American Battlefield Trust.  He looked especially at "Declarations of Causes" documents that four of the Confederate States added to their articles of secession.  The documents from those states (South Carolina, Georgia, Mississippi, and Texas) showed both slavery and states' rights as the two predominant themes.   As to the issue of a state's right to leave the Union, Pierce summed up the theme from the primary documents this way:  "The states argue that the Union is a compact, one that can be annulled if the states are not satisfied with what they receive in return from other states and/or from the federal government."

in the 1900s, the united states was still a largely agrarian society with a very fast growing industrial and manufactering sector.

the south of the country was the bread basket of the country with large farm lands making up a majority of the economy.

in the north and more specficially north-west, growing manufactering and export sector had made the united states into a powerful exporting country.

this peaked in the 50s and 60s when the united states became the largest economy in the world and the largest exporter.

today, the majority of the united states economy is made up of the services sector that includes banking, insurance, music, movies, hotels etc.