They fought over the moral issue of slavery.
Butt this is what google told me xD
They fought over many reasons like...
Industry vs. Farming. ...
States' Rights. The idea of states' rights was not new to the Civil War. ...
Expansion. As the United States continued to expand westward, each new state added to the country shifted the power between the North and the South. ...
Slavery. ...
Bleeding Kansas. ...
Abraham Lincoln. ...
Secession. ...
Activities.
D would be the correct answer
The South opposed the Wilmot Proviso because it would have prevented any new territories from having slavery in them.
In 1846, Congressman David Wilmot of Pennsylvania introduced the proviso as an amendment to an appropriations bill in connection with the peace treaty being negotiated with Mexico. His amendment stipulated that any territory gained from Mexico would be free, not allowing slavery. The specific language of the proviso went like this:
<span><em>Provided, That, as an express and fundamental condition to the acquisition of any territory from the Republic of Mexico by the United States, by virtue of any treaty which may be negotiated between them, and to the use by the Executive of the moneys herein appropriated, neither slavery nor involuntary servitude shall ever exist in any part of said territory, except for crime, whereof the party shall first be duly convicted</em>.
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Wilmot's amendment passed in the House of Representatives, but was unable to get approval in the Senate. The high-intensity debate over slavery and the expansion of slavery was evidenced by how things went with the "Wilmot Proviso."
The United States feared that if communism was successful on Vietnam, the rest of the countries that border it would soon turn into communism and those other countries that border that new communist country would also be converted to communism and so on. This is called the "domino theory" and made the United States to send troops to prevent the theory from happening.