<Tr> <Td> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> </Td> </Tr> <Ul> <Li> </Li> <Li> </Li> <Li> </Li> </Ul> <P> Historians debating the origins of the American Civil War focus on the reasons why seven Southern states declared their secession from the United States (the Union), why they united to form the Confederate States of America (or simply known as the "Confederacy"), and why the North refused to let them go . While most historians agree that conflicts over slavery caused the war, they disagree sharply regarding which kinds of conflict--ideological, economic, political, or social--were most important . </P> <P> The primary catalyst for secession was slavery, especially Southern political leaders' resistance to attempts by Northern antislavery political forces to block the expansion of slavery into the western territories . Another explanation for secession, and the subsequent formation of the Confederacy, was white Southern nationalism . The primary reason for the North to reject secession was to preserve the Union, a cause based on American nationalism . Most of the debate is about the first question, as to why some southern states decided to secede . </P>

What is the main reason the us civil war started
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