Between 1820 and 1850, which trend most contributed to growing intensity over the issue of slavery?

The issue of slavery becomes more and more divisive.

2686-2181 bce-- "egyptian civilization developed along the nile river in large part because the river’s annual flooding ensured reliable, rich soil for growing crops."

1069-664 bce-- "ancient egyptians developed wide-reaching trade networks along the nile, in the red sea, and in the near east."

the