The best response to the question about how the result of the Civil War in the United States differs from the civil wars in Cuba and Vietnam is:
C The wars in Cuba and Vietnam resulted in a completely new government being instituted.
The U.S. Civil War primarily focused on issues of slavery and states' rights, leading to the preservation of the Union and the end of slavery, but it did not result in a new government. In contrast, both the Cuban Revolution and the Vietnam War resulted in the overthrow of existing governments and the establishment of new regimes.