What was the significance of the Mexican-American War in creating conditions that eventually resulted in the American Civil War?

In my opinion, the importance of the Mexican-American War
was that it destroyed the compromises between North and South that had previously been
established.  By doing so, it reopened the arguments over the extension of slavery. 
This caused the North and South to grow further apart and finally
split.

Before 1846, the Missouri Compromise had more or
less solved the issue of the expansion of slavery.  But now, the war threatened to bring
more land into the United States.  Significantly, all this land would be in the South. 
This made the North very suspicious of the war and of the motives behind
it.

Once the land was taken from Mexico, a debate arose
over whether it would be free or slave.  The process of debate led to such things as the
Compromise of 1850.  This debate, as I said, reopened the suspicions that the two
regions had of each other and forced them to argue once again over the extension of
slavery.