How did the mexican war lead to the civil war?

It did not lead to the Civil War, what led to the civil war was the war of 1812. That was when U.S.A recognized that it needed to become stronger, and slaves were transported to the United States and put in the working class under bad conditions. Child labor and prejudice began there as well.

the war was the westward expansion of the United States. All through the 19th century Americans believed it was their right to expand westward. At the time they believed they could conquer the people already living on the land and take it for the United States.

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