What is the significance of Wilmot Proviso?

The significance of the Wilmot Proviso is that it helped
to make the North and the South more angry at each other at the time of the Mexican
American War.  It did so by helping to cast the war as one that was about
slavery.

Many in the North worried that the point of this
war was to take more land that would (because it was in the South) become slave
territory.  For this reason, they (a famous example of this is Henry David Thoreau)
opposed the war.  The Wilmot Proviso helped to publicize this idea because it stated
that no land taken from Mexico could become slave.

The
Proviso did not pass, but it still served to make the North and South come into conflcit
more.  This helped to bring on the Civil War.