Using the time frame 1800-1849, argue that 19th century American history can be explained by sectionalism.

There were many incidents in the time frame that you
mention that show that American history was being driven by sectionalism.  I will
mention three of those incidents here.

First, there was the
controversy that led to the Missouri Compromise in 1820.  This showed that the two
sections of the country already felt at that time that it was vital for them to have
equal representation in the Senate.

Second, there was the
Nullification Crisis of 1832 and 1833.  This showed that the South felt that the North
was ignoring its needs and that the South was willing to more or less break with the
Union in order to get its way.

Finally, there was the
Mexican-American War.  To some extent, support for this war broke down along sectional
lines.  Many Northerners opposed the war because they thought that it was being fought
solely to gain more territory for the slave states.