What three political issues led to conflicts between the north and south in the early 1800s?

One thing to
remember is that economic issues are always political issues. In the early 1800s the economies
of the Northern and Southern halves of the U.S. began to diverge because while the North
diversified with industry and trade, the South continued to be reliant on agriculture and
therefore, slavery.

The second key to your question is the Wilmot Proviso.
This was a bill that would have banned slavery in all of the new territories gained from the
Mexican-American War. The Northern states (who had a majority in the House of Representatives)
wanted it to pass, but the Southern states (who ruled the Senate) did not allow it. After this
legislatory skirmish, the Free-Soil Party was founded, thus bringing the issue of slavery to the
forefront of Congressional politics.

The last thing to keep in mind is that
the Southern states were very concerned over the admittance of California to the Union.
California wanted to enter as a free state, but its arrival would put the Southern slave states
in the Senate minority. The Compromise of 1850 briefly settled the issue, giving California
statehood. However, it allowed for greater control for slaveowners in the South, thereby
exacerbating the slavery issue even more.